In the arcane and niche world that is the intersection of peak bagging and ham radio, aka SOTA, the participants fall into two broad groups; activators and chasers.

Happening daily across the planet, activators, especially the apasionada, ferret radios to wild and distant peaks, setting up a temporary radio station and then hoping that the co-dependent chaser community hear, respond and make the trek worthwhile. All things being equal smiles abound.

Within this rarefied world is another notable accolade where activators assume a dual role of activator and chaser. The chance to communicate from one peak to another is special in that two apasionadas get to experience what their weak and faint signal must sound like to chasers but unlike most chasers get to do it in a “electrical” noise free environment. Often a faint and perfectly audible voice from a distant location plays in the headphones. This contact unsurprisingly is know as a Summit to Summit (S2S).

Some in our community are legendary in the pursuit of S2S contacts such as Colorado based Cary (KX0R) and Dave (N6AN) here in SoCal.

Sadly, I’m not one of these legends nor anywhere close.

As with many activators, my initial goal was to attain the coveted Mountain Goat award which in true Western style I achieved in a respectable two year window having shlepped my gear up 100+ mountains. The equivalent chaser award, Shack Sloth took me over seven years to achieve through only S2S contacts, no comfy chair for me!

Truth is I’m never quite as aware as I could be about other activators concurrent efforts and pretty much all my S2S contacts have been others calling me.

I love to mix up my hobbies and pondered the practicality of applying technology to my deficiency.

I kicked the tires on an idea, in hindsight possibly overkill of creating a small PC centric solution for the 2023 G/LD event that Mark M0NOM organized. Reasonable progress was made but I became distracted and then further distracted with a return to the UK.

My morse code dabbling has spurred a re-interest in past projects primarily to complete and/or use some of what I’ve done in the past.

Green for go!!

Peaks can be cold, dusty, beautiful and throughly inhospitable. Two problems exist that limit my S2S enjoyment; awareness and too much fiddling to get on frequency.

Improving awareness could be as simple of an LED lighting up or possibly a bank of LEDs conveying opportunities immediate and those slowly drifting into history. A green LED could indicate a new and current S2S opportunity, yellow some or one that are aging out dictating prompt action and red for opportunities that are most likely missed.

Less fiddling might be a winner

On a busy Saturday, details of activators scroll by on our notification web site in a random and jarring way. I’m reading one, checking the time, frequency and suddenly the line is displaced down one or two or more slots. Lost, I attempt to regain acuity and give up in my transliteration from web to frequency readout on my radio. Another S2S is missed.

Tailored for my iPhone screen, a list of current activations is displayed with a color coding to denote age matching the LEDs. Sorting them narrows to band (maybe 10m for the current 2024 challenge), geography, calls, mode etc.

Quickest way from A to B

Once upon a time people paid me to write software.

During the dawn of computing we used a gamut of languages from labor intensive assembler to one of a multiple of block structured languages and even the grand daddy of “object oriented” in the form of Simula 67. As someone, that was ejected into the ranks of shepherding software engineers, I often lamented at how long software development remained in what appeared an efficiency neolithic age. ChatGPT has dispelled that notion but along the way graphical almost cartoon like systems have surfaced.

As a quick and efficient way to develop a working system, Node Red is actually quite easy to master and satisfying in the immediacy of usable software. Maybe not appropriate for large scale mission critical system, it never the less has a real and valid place.

Zeros at 7 o’clock

Raspberry Pis come in many shapes and forms but alas have been far too hard to find for far too long. Rummaging through my “junk box” yielded a Pi Zero W, forgotten and feeling inferior to the newer and unobtainable Zero 2 W, its pressed into serviced simply based on its size and ability to sit neatly on my newly established “flight deck” aka a clip board.

The Pi OS comes in two or three flavors one known as “headless” but unlike a Zombie can be counted on to do useful things. Installed along with Node-Red on my forgotten Pi Zero W and it’s single USB serving as a conduit to the CAT interface on my KX2, I’m off to the races.

In addition to QSY-ing to a frequency, pressing CALL with send W6PNG in morse or S2S an declaration of opportunity.

LED Duration

On that same busy Saturday, it’s plausible that the Green, Yellow and Red LEDs are on all the time somewhat negating their value. I need to experiment with durations which could vary depending on time of week or an event. For example, maybe on a busy day green is only for displayed ….

Predicated on cell service

Cellular service is seemingly everywhere even in remote parts of the Western USA especially atop a peak. However, a peak’s height and hence reception of/by multiple towers can confuse things such that we often end up with no cellular service. Go figure.

I’ve learnt that sometimes it’s worthwhile to pause, try something and then consider refinement and next steps. There’s lot of things I could do beyond determining if the current prototype is usable and useful.

Certainly this work/project has been a great complement to hiking in that it’s a brain work out.

Any comments, thoughts, suggestion or ideas how to evolve this little project are always welcome.

The arc of radio kits is waning.

Easy to work with parts are going out of production in deference to tiny, minuscule equivalents that are a machine’s dream.

Many wax and wane about the glory days of Heathkit, that American landmark that defined a small corner of 1960s American history. The mantle is passed, grabbed or offered and Elecraft catches it and define their own place in kit history. Better than Heathkit, similar build detail but simply a better performer.

Truth is, a high percentage of electronic kits end in tears. Good intent isn’t sufficient to win the day.

Somewhat like driving on a windy mountain road, success is a function of paying attention and staying between the white lines and so build details are a key success determinant.

I hadn’t really intended to go to this party as I’ve never really been a “morser”.

I did attend a different Elecraft party, by buying and building a K2 replete with a family of add-on modules. Hard work but the results still hold their own 20 years on and a life time of new technology to out do the little K2.

Last orders have been and gone. Kicking myself but now “happily” paying over the odds to someone that was quicker off the mark than me and I now have a K1 kit with a small family of add ons.

Remember Covid? Who doesn’t!!

Stuck at home and wondering what has happened to my travel centric life, I turn inward, pull out my K1 kit, power up the soldering iron and relax into a final journey. Screw this build up and no replacement is in sight.

Analog radios are essentially math machines. All those capacitors, inductors, transistors etc are simply crunching on RF signals, pulling out, suppress some, amplifying others to the point that something “intelligible” pops out a speaker or headphone. Analog radio designs are old dating back into the 1920s and 1930s. Different designs and approaches have been pioneered and some stood the test of time.

Eric and Wayne love one of those design approaches, termed “superheterodyne”. It’s in the K2, the K1 I’m about to tackle, the K3 and even the very recent KH-1. It’s a fine approach defined by copious parts count and great performance. The value of the designer is to align all the resistiors, capacitors, transistors, etc into something that is optimized for size, cost and performance. Think tubes of paint and imagine a painting by a five year old versus that by Cezzane. Both start with the same raw material but the end results are markedly different.

Buttons, I love buttons. I’ve long thought about this passion for buttons and knobs and irrefutably tie it to far too many visits to the Science Museum in Kensington, London as a “wee knipper” during the go-go 60s.

Eric and Wayne don’t just love super-heterodyne designs but modular super-hets. Filters are an essential part of any radio both to improve its performance but also to meet FCC requirements to be a good HF citizen and not create unnecessary interference.

As amateur we have access to many bands, shortwave and beyond. The K1 design separates bands into “insertable” filter boards that support 2 or 4 of a limited subset of shortwave bands. It’s a build time decision and my eBay special came with a 2 band filter board that I opt to build for 80m (a night time band) and 40m (a jack of all trades band).

Building the main board….

Possibly overkill but a wonderful peace of mind and potential time saver, I methodically test every and I mean every component before I solder it in. Resistors are checked that the value matches what is demanded, transistors are verified as handling might have zapped a part of it, joints are verified for connectivity and yes, I’ve found dud parts, I’ve found wonky joints and feel all the better for this obsessive attention to detail. Time is never abundant but this journey should be savored and made all the sweeter by a “safe” arrival.

Weeks turn to months and months into years. Under appreciated and under complete, a shoe box emerges with an almost complete ATU. Distracted and pulled away onto house projects, consigned the almost ATU to an ignominious plastic home.

Wire wrapping Dunkin’ Donut like miniature rings, installing a few more components and magically I’m done. Three years in the making and the sense of completing an incomplete project is an additional reward.

An unexpected QA member verifies what I have built, listens for tell tale relays clicking as a match is sort and a wink and a thumbs up convey this build journey hasn’t ended in tears.

Well done me!

Time well spent and a very enjoyable build.

It’s a wonderful little rig but technology has marched on and the KX2 in most all respects remains my “go to” radio for SOTA.

However, it’s a keeper and to borrow a line from Charlton Heston….“from my cold dead hands….”

I’m spoilt.

It’s not that I was born with a silver spoon in my mouth, I wasn’t.

Nor is it that I live in California as it’s not unequivocally the Golden State anymore.

It’s simply that we live in an age of abundant digital maker products.

The most recognizable in this niche world might be the runaway British success that is the Raspberry Pi.

All good history buffs know the Romans made remarkable things long before north Europe was “civilized” and so it is with the Italian Arduino boards that brought us the word “Blinky”.

What makes this a Golden Age is the accessibility to not just boards but boards at price points that in some cases are as cheap as a cup of coffee but also the abundance of supporting material that allow a broader audience to successfully own, use and adapt this potpourri of gems.

While Brits and Italians might be unlikely movers in this digital revolution, the landscape is very global with not just a strong leadership from the US but a remarkable Chinese component.

My entire adult life has been spent in and around tech. The first whopper of a computer I used as a student had little donuts wired together by amazingly adapted humans that was its central run time memory.

We’ve come a long way from the nostalgia piece above.

An oasis of abundant opportunity for me and all the way down to kids in every school and almost every home.

Now that’s a Golden Age!

Station automation, an unlikely interest area ….for me

My first exposure to the need and value of station automation came during a trip to Prince Edward Island, Maritime Canada in 2018. Renting K6LA’s station was a journey into an Aladdin’s cave of radios and gear. I was fascinated.

In my quest to touch as many bases, I broadly wanted to build a “learning bench” for ham radio station automation. With so many options and avenues, I decided to use the Feather family of boards from New York’s unusual success, Adafruit. These standardized and not surprisingly small boards have a fixed form factor and standardized pin out configuration while offering a huge mix of CPUs and interface/connectivity options. Exactly what I need for my station automation learning bench that presumably needs various communication methods, expand-ability and various ways (switches, screens etc) to interface and communicate intent.

Documentation and examples wins the day

The battle Royale between Motorola and Intel in the 1970/1980s was won hands down by Intel and not through having a better design (they didn’t) but through having an amazing support system for designers and manufactures with detailed documentation, examples etc etc.

This is what makes Adafruit so attractive to me and in consequence I’m happy to pay a premium versus an eBay or Amazon el cheapo clone/knock off/look alike.

Whether it’s a Jeep borne or plane borne radio station, small, light and rugged are keywords for gear and many commercial systems fail the small and light metric. Wires galore is another aspect of ham radio and this is somewhat a hassle when assembling a portable/transportable radio station

My “learning bench” therefore is aimed at using digital maker technology to reduce, streamline, make more redundant/resilient some of what I’m dragging around in the hold of a plane or the roof of my Jeep.

Twiddling gear with 12v

Any radio that finds itself in close proximity with others quickly finds a medley of filters, switches etc being brought into play to protect one radio from another. Radio receivers are stunningly sensitive devices often multiplying a weak signal a million fold to extract a voice and conversely a radio transmitter, typically feet away from the receiver is pumping out huge amounts of energy that could reek havoc in a receiver.

The “standardized” method to instruct automated filters, switches etc that make up the safe separation of receive and transmit signals is by twiddling voltage to either zero or twelve on pins tied to certain functions such as engage a 10m filter, or engage a 40m filter or route radio waves from this input to one of many outputs.

With this in mind one half of my learning work bench would be a platform to assert twelve volts on different connectors attached to an automated filter, automated switch etc.

Having built one before and wanting to do better and staying within the spirit of learning more, I decided to design a simple board using KiCad, freely available software and have my design manufactured by a service in the US. Once I have my board/PCB, it’s my job to populate it with whatever my design dictated in the way of chips, transistors, resistors etc.

Splitting things.

Part of my premise is that too many wires and cables exist that connect station gear together and as more gear is added, neat and tidy becomes a rat’s nest. In a “permanent” station this can be hidden and typically once done, isn’t reconfigured often. In the Jeep or DXPedition world, the station is being constructed and de-constructed every time.

In my photograph above of the Stack Match and associated black control box, the thought is to split the black control box and locate the 12v twiddler functionality next to the Stack Match and “remote” the front panel (used to select antenna combinations) to a “control head” either being a world of buttons or a Node Red accessible.

The connectivity between the 12v twiddler and control head could be one of many including WiFi (my favorite), LoRa or even wired ethernet or CanBus.

Remote “control” side of my “learning bench“

As a kid growing up in London in the 1960s, I vividly remember seeing NASA’s Mercury capsule on display at my ever favorite London Science Museum. Buttons and switches everywhere and with them a lasting love was born to press things.

Decades later the passion is still strong and I design another Feather centric PCB that has 18 buttons and a 3.2” touch screen. My left red, grey, green stack is used to “instruct” my remote 12v twiddled attached to the Stack Match to select one or two antennas with various phasing options.

Step one – design and prototype

Google can be your friend and searches throw up everything from ideas lost in ads to ideas so succinctly shared that it’s a joy to borrow, enhance and experiment my way forward.

Free to you, free to me

While it’s fashionable for some to deride large US tech companies, truth is they pioneer a lot of advanced software techniques and tools making many available for free. Maybe less altruism than pragmatism and being pushed by the open source movement, either way we the community (both hobbyist and commercial) benefit.

Microsoft’s Visual Studio has long been considered a professional grade development environment and the “community” edition has more features than I’ll probably ever master but its my go to for embedded development were possible.

Step two – Learn KiCAD

Day one is always intimidating when tackling something completely new. As I really had no idea what level of sophistication was needed in a PCB design tool, I shied away from Autodesk’s Eagle product as the free looked too feature restricted and I plunged headlong into an oddly successful European piece of free software called KiCAD.

YouTube can be your friend sometimes and it’s hard to get radicalized watching software tutorials. A slow and often painful iteration of watch, pause, try cycles day after day eventually got me to a design I thought might actually work. Success is much more than transcribing an electronic circuit design to KiCAD’s visual language as ultimately it’s about manufacturability. Parts and especially similar ones (such as a connector for headphones) come in a mind boggling variety of subtly similar packages. Ensuring my choice has the correct dimensions for pin separation is critical. If my board expects three pins from my headphone connector arranged in a straight line but I order one with them in a triangular layout, I’m screwed.

In the States we are spoilt in having electronic parts stores that literally carry 100,000s of components (at least pre Covid). Parts acquired and time to be patient as I wait on my PCB.

Step three – outsource to PCB manufacturer – OSHPark

Hobbyist PCB manufacturing has transformed from etching copper with toxic chemicals that not only are harmful but hard to dispose of practically to a world of remarkable choice driven by the Internet. With a standardized language to define how to manufacture a PCB, options for boards in my hands in days from China exist through to more prosaic US manufacturing taking weeks. Philosophically believing in supporting local and domestic businesses, I opted for OSHPark. Used and loved by many hobbyists, I submit my design, share credit card details and sit back for what seems an eternity and then 21 days later its just like Christmas.

Step four – Stuff those boards and success!

Successful PCB design is a little binary in that the smallest issue or error can render the project an abject failure. Diligence, checking and rechecking prior to submitting the design to OSHPark paid off and after rather joyfully stuffing and soldering buttons, capacitors, connectors and all manner of mundane garden variety components, first power netted success. Issues did exist but were easily remedied with a little solder and wires.

A better, more contemporary button cluster and LCD…Node-Red

I recently made a serious effort to master the fundamentals of Node-Red. Simplistically, it’s an easy way to create applications with visual display/interaction accessible via a web browser. Node-Red could run on my contest logging computer that has limited free real estate and could serve up a web page to control a “distant” WiFi connected 1703. In essence the iPhone is replacing my remote control head with my 18 buttons and little screen.

What’s next?

This has been a fun start to a journey. Learning is rewarding but it’s even more rewarding when the designed boards pretty much work.

An obvious next step is to experiment using a low pin count M0 ARM CPU chip or even the new RPi 2040. Enormous amounts of reference designs are available to help me along. However, ideas seem to begat too many other ideas and the world of LoRa is interesting in of itself.

Grounded.

No travel, no vaccine, no toilet paper, no eating out and for some no work but for me these deprivations come with copious amounts of time to reflect on life and turn this into something positive.

Maybe it would easier to just rent a house.

Even if you find one that looks promising, it’s still quite possible that it’s cramped, or noisy or worst still, the spectacular mountain view that the owner is convinced is a deal closer, blocks those weak singles that this is all about.

We are all creatures of comfort and having spent countless hours clamoring to remote and sometimes hostile peaks, setting up and operating under the elements, the idea of a Jeep seemed so obvious and seductively appealing. What could be simpler, thought this perennial optimist.

After all, a cooler can come filled with beer, cheese and crackers. Sleeping in the Jeep offers a quicker deployment solution to a tent and far more practical in defending against scorpions, snakes and bears.

I’m chastising myself for not seeing this sooner but lock downs has our mind set skewed.

As a wilderness mountain top radio guy, I’ve gone beyond awe, as to the practically of the Elecraft KX3 radio system. It’s modular, you can add a gizmo (PX3) to visualize the airwaves ensuring I find contacts quickly and I can be a real player with the outboard signal amplifier (KXPA100).

I’d sort of refined this almost to the absurd on a trip to St Kitts in March 2020.

It’s a long drive up 395 east of California’s Sierra Nevada mountains. Dust bowls that were once lakes come and go. Whitney is straining to ensure you see it really is the high point in the lower 48 and Mt Rainier is simply a wannabe. A solitary guard tower is a reminder to a different mind set in a different era. Marijuana is available on tribal land just off of 395 and eventually the road lurches east across the state line and into Nevada.

Time counts in contest.

Borrowing One by One callsigns is a fun privilege with the added advantage of declaring yourself quicker than saying W6PNG or M0SNA.

My real player station isn’t really that. I’ve compromise on antennas and one is an abject failure.

My Jeep dash looks cool with the KX3 and PX3 plus a great view. However, the sun is relentless and with my nose facing west to admire the view, the afternoon progressively becomes more and more brutal.

My less than stellar performance in Nevada as K7E hasn’t really deterred me. Years ago, Ken Zaremba, my then boss described me as tenacious. As it came with a smile, I said thanks and promptly looked the would up in the dictionary. I liked the descriptor.

Four Days in Purgatory…W6E in the Mojave Desert at 98F

Game on and the KX3 is replaced by its more manly sibling the K3s, the puny 100 watt amplifier by an equally manly 500 watt beast and my menagerie of imitation antennas by at least one real antenna, a 10/15/20 HexBeam supported by something that wouldn’t deliver a repeat of my afternoon telescoping, from 30 ft to 6ft in 3 seconds.

I find myself not sitting with my radio in my Jeep at 8,000ft on Frazier Mountain but rather in the flat, arid Mojave desert. Summer 2020 in California has been fire after fire after fire, to the point that I wonder if after a decade more of this if anything of California’s wilderness will be left. I’m still in the front seat but with my nose pointing east and neither my radio nor super sized amp are anywhere less inconvenient than the drivers seat.

I make futile attempts to block the sun with clothing, bedding etc but I’ve never so wanted the sun to set.

Starring into Scott’s ex TV van makes me realize my Jeep is really just a mobile ghetto that is in need of some serious …..

I’m inspired by a Cow that is Scott’s Wilderness Lounge

The 35″ tires aren’t really necessary especially if your lead scout for a TV van designed for modest off pavement work. Truth is a Rubicon just looks more convincing with them. However, the batwing awning is a real plus and over time I add side panels.

With shade and additional stowage addressed, my attention turns to a better operating location. My preference is still the front passenger seat but space isn’t practically available to mount the K3/P3/KPA500 without “removing” them and at the time the K3/0 was (and still is) a piece of unobtanium.

After experimenting with being a bit of Jeep baggage in the stowage section its clear neither that works nor the front passenger seat.

A more boutique solution is required.

Having flown in excess of 2.5 million miles, tray tables occupy an odd space in my pysche. The drop down ones make me think of too many hours in rif-raf class but some variation of that seems appropriate given my space constraints are similar to what the tyranny of airline executives hath wrought on passengers.

My neighbor Mark loves to brainstorm “construction” solutions.

Our first attempt is actually quite effective and a million times better than upfront in the gold fish bowl in purgatory.

Mojave Desert shake down during CQWW WPX CW May 2022

CQP 2022 – Frazier Mountain

Littering the desert and mountain camp sites

At first I thought it was odd.

Pink boxes here, yellow ones there, black ones, small ones, large ones and a cooler almost as large as my Jeep are scattered around the desert and the mountain. The choice of color aids quick identification and presumably pink is one tenth the cost of a manly black or classic yellow SAR.

Jeep interior is small and certainly not Dr Who’s Tardis

After two trips I realize the wisdom of pink boxes in the desert as I seem to spend for ever moving things around the Jeep either to find something or to relocate while something is put in its “permanent” place such as the radios, amp or even my sleeping mattress.

It doesn’t work. Too much time and energy are spent and I need to transport things roughly where they will be deployed. Better still I should bring less as I don’t quite have the room Scott has for boxes galore.

Table iteration two..wires in situ, mounting points for tablets

It’s almost three years since my epiphany and summer plans dictate that any CQP 2023 refinements be done now.

After re-thinking Drew N7DA and Matt K0BBC time with the table, I felt that keeping the back seats fully up would give people more room to slide out from directly in front of the in flight dinning table.

Speed of deployment was another goal by reducing the time spent rummaging for (and packing back up) wires, connectors etc. It seems trivial but truth is setting up the station with antennas can take 4-8 hours and any savings especially if in many areas add up to something meaningful and much appreciated under the cruel bright western USA sun.

A huge science project with no limits nor end?

Clearly this is a direct result of Covid as in a better would it would have been St Kitts again, or Saba or St Martin and not the back of a Jeep but I’ve done something tangible to expand my operating options away from my RF challenged home.

With that in mind, I need to draw the evolution of the Jeep station to a close and enjoy what I have.

….but I’m a dreamer and an optimist and still have flights of fantasy around an “how easy” an M/2 HP setup would be, however my “Fields of Dreams” has been a hard sell to others particularly around the Jeep being fine for one but possibly not two.

What’s clearly apparent to me is I love making things, learning about new areas including station design and automation, as much as I do operating what I’ve built or learnt about. It truly is that the joy is the journey as much as the destination.

We’re hurtling toward the peak of Cycle 25 possibly 3 years away and then its downhill into the abyss of limited propagation and even more limited easier long distance contacts.

I don’t want to look back saying I could’a, I should’a…

There are times when you wonder if your receiver and antenna are really working as they should. The band is dead, or empty, it’s the middle of the day, the D-Layer is sponging up every radio frequency excitation. Perhaps you can hear a few signals, but they are fleeting — and you need a steady and predictable signal source for a proper test. An RF signal generator will give you a steady carrier, but there are times when you’d prefer to have a true CW beacon to tune onto. This simple, general purpose multiband CW beacon can be run up on the frequency (or frequencies) of your choice, is powered on a 9V transistor radio battery, and can moved to attenuate to the desired signal level, for radio receiver system testing purposes.

This beacon transmits a hard-coded message in morse code on any frequency supported by the si5351 (10kHz to 160MHz). The code targets an Arduino Nano, Uno or bare ATMega328P and an si5351 breakout board. No display is necessary. You can add one, and controls, if you like. The code includes a simple CW keyer for manual sending (not used, but left in place for this application).

Any number of frequencies in the HF and VHF range can be specified by adding them to an array of transmit frequencies. The beacon iterates over the array and transmits the message on each frequency in sequence. The beacon’s CW speed is configurable. Sidetone is available as a 5v square wave on the D7 output. There is no support for switched low pass filters but this would be easy to add.

The Github repository is here.

There’s a reason why most homebrew transceiver kits and scratch-built projects are monoband and single mode — theres a chance you’ll finish it, or at least, get it working for a while. Building a multiband HF transceiver is a big job, as any homebrewer who has attempted it will tell you. It may take years.

My build of Eamon EI9GQ’s transceiver is no exception. It was started in 2018, the first rush of enthusiasm resulting in a working superhet receiver on 160 to 40m, and boxed up in a custom solid aluminum case. This video shows it off circa 2018.

With a heap of work ahead, and a list of unresolved minor problems, other projects took priority, and the rig ended up spending the next four years in a carton (with all my notes, schematics, assembly and PCB sketches, and unused components). Until recently.

Schematics

It’s my normal practive to include kicad schematics, but in this case the EI9GQ designs are copyright RSGB. So go and buy Eamon’s book from the RSGB Bookshop, or on Amazon, you won’t be disappointed.

Resumption

E-mail discussions with another keen maker (Neville ZL2BNE) about his build of this transceiver gradually tickled my interest to resume. Nev was making good progress, had his rig transceiving, and was working QRP DX. I dug mine out of its carton and fired it up — it had all the appeal and problems that I remembered from 2018. I resolved to kick it along the road for a bit, to see how much interest I could reconstitute. Upon resuming, a number of issues needed addressing, some easy, some repetitive, some more difficult but not impossible. Here are those that I can remember…

Firstly, the 9MHz IF amplifier oscillated with the manual AGC turned up, and was generally unstable. To fix this, I put a 5k5 resistor in parallel with the drain tuned circuit — a well known technique for taming high gain stages. I figured that of the three identical 15 to 20dB gain stages, it made sense to damp down the gain of the first stage. This did the trick, and all three stages exhibited a nice resonance peak using the trimcaps, and overall stability.

The next thing was to calibrate the si5351, a simple job I’d never bothered to do, resulting in the display showing odd and fractional frequencies for the property resolved SSB stations in the 2018 video. If you want to know how this is done, go to your si5351 library’s README file, it is quite easy to do, and once done, lasts for years, or for ever.

Next problem was the LCD backlight. The large font 20×4 LCD I had chosen for this rig was a bit of a novelty back in 2018. I liked that it’s huge characters could be read from half a room away. I used to joke with myself that I’d still be using this rig in my 90s, when all the compact rigs with fiddly little OLED displays were beyond my failing eyesight. And the four lines of 20 characters gave me extra display space for luxuries like a UTC clock and metering. But that big display had an equally oversized backlight which could light up a darkened room, but drew more than half an amp. Although this rig was intended for the shack bench, I was not used to my receivers pulling over an amp.

I decided to multiplex the LED array with a simple PWM LED dimmer, which uses one half of a 4093 quad gate as a variable duty cycle oscillator running at around 70kHz, driving an IRF540 FET switch. This worked a treat and the dim potentiometer was mounted right on the front panel. It controls the backlight from off to 90% on, when it drawn around 500mA.

The next mini-project was an AM detector. I was not interested in full AM transceive capability– I have other homebrew projects for operating VK legal limit AM — but I did want to be able to enjoy decent AM reception using the high quality 6kHz filter in this receiver’s set of three KVG crystal filters. I chose an infinite impedance AM detector, successfully used in a prior AM receiver project.

This mod necessitated making a PCB to overlay the existing product detector and audio preamp, with a plug-in board containing the AM detector, it’s own preamp, a miniature relay to steer the incoming IF signal to either detector, and a shared 4046 quad bilateral analogue switch which selects the product or AM detector’ s output, and additionally does receiver muting and Sidetone routing when in CW transmit mode. This assembly worked well. One hickup — I originally left the BFO powered up in AM mode — and even though there was no direct BFO coupling anywhere, there was more than enough stray coupling to resolve sideband. This was fixed by switching the BFO board’s DC power off in AM mode.

The next task involved coming up with a mechanism to select one of the three KVG (ex TelRad) filters. These high quality 9MHz crystal filters were common on eBay a few years back, and are a feature of this receiver. These filters came in a set of three. In a slight departure from superhet convention, a separate filter is used for USB and LSB, with a 6kHz AM filter in the middle. The BFO runs permanently on 9Mhz. I wanted to have filter selection under software control, so that the correct sideband filter would be selected for the current band. One of the front panel pushbuttons was used for a mode control — pushing it cycles thru the sidebands and an AM setting. A small daughter board was added to the filter assembly containing a PCF8574 demux IC on the I2C bus. A few additional lines of code implemented a simple control function.

The 2018 receiver’s front end board included space fo r an RF amp block, with a pair of miniature relays to bypass it. The original PCB was layed out for a MMIC which probably would have worked fine but in the end I built up one of EI9GQs broadband RF gain blocks using a parallel pair of MPSH10 transistors for around 20dB of gain. The EI9GQ amp was built on an overlay board sized for the available space.

A few minor additions followed. A 41MHz Low Pass Filter was added on the VFO buffer input. On the highest band (28MHz) the VFO is 9MHz higher, on 37MHz. This low pass filter cleans up any VFO harmonics, probably low anyway, but a safety precaution.

The diplexor was added, a balanced tee arrangement, with series and parallel 9MHz tuned circuits arranged to pass through 9MHz energy, but sink all other frequencies into 50 ohm resistors. This ensures proper termination of the receiver mixer and keeps unwanted mixing products, particularly at the image frequency, out of the first IF amplifier.

One of the nore repetitive jobs (which just has to be done!) is making and tuning up the remaining Band Pass Filter modules. Three mire were built, for 17, 15 and 10m, using the EI9GQ design. This gave eight bands, 160, 80, 40, 30, 20, 17, 15 and 10m. My approach to the last three boards was mostly as I’d used in 2018, other than improving the use of right angle 0.1″ header pins inserted through a row of holes drilled through the PCB for mechanical strength.

Next job was a small board mounted on the rear panel next to the two SO239 sockets. This board has the transmit-receive relay, and a second relay that switches between two SO239 for an Antenna A/B switch. Three 7812 regulators supply the three supply rails, 12v always on, 12v receive, 12v transmit. All three unregulated DC supplies are available on headers as well, to avoid heavy current being drawn thru these regulators, such as the transmitter PA and the LCD backlight.

The rear panel has two antenna sockets (for A and B antennas, switched from the front panel), a panel XT60 socket for DC 12V, and a set of 3.5mm and RCA sockets for connections (external muting, paddle, external speaker, and an auxiliary RCA, as yet unassigned). These 3.5mm switched stereo sockets are very useful pieces but unfortunately are not long enough to go through a 3mm aluminum panel. The best solution is to mill out a recess larger than the socket, but that requires a milling machine that I don’t have. So the workaround was to cut a rectangular hole in the 3mm rear panel, and bolt on a 1.2mm aluminum plate to hold the sockets. Its easy to paint and label this small piece.

Preview of the Exciter

To turn the EI9GQ receiver into a transceiver I needed a microphone amplifier, balanced modulator, transmit mixer, T/R switching, a PA stage and LPF set. Back in 2018 I built Eamon’s LM324-based microphone amplifier (a design out of EMRFD) and another hand made diode balanced modulator. All of these mixers use 1N5711 Shottky diodes individually matched to within a millivolt on the diode test setting on my digital multimeter. The transmit mixer is another hand made diode ring mixer, this time an unconventional triple balanced mixer.

The PA chain after the transmit mixer will be MPSH10 x 2, 2N5109 and a pair of RD16HHF1s for about 10 watts 160 to 10 meters. The LPFs will be by Eamon, derived from the original W3NQN designs, each filter on its own plug-in board, relay-switched at either end, filter selection via another PCF8574 on the I2C bus. There will be six LPFs (for 160, 80, 40 and 30, 20 and 17, 15 and 10 meters).

What’s next?

If you’ve made it this far, thanks for reading, feel free to leave a comment, and stand by for the third and final post on this transceiver project, which will address completing and commissioning the SSB and CW transmitter stages.

Weak Signal Propagation Reporter is a global radio propagation monitoring and reporting network comprised of thousands of low power beacons operating on the amateur radio bands. WSPR beacons can be detected from the lowest of Medium Wave frequencies (137kHz) all the way through the HF spectrum (all the bands from 160m to 10m are popular) to the VHF bands, 50 and 144MHz. WSPR receivers decode the tiny beacon packets and upload them to a central database, at WSPRNet.org, where anyone can literally ‘see’ the propagation paths that are currently open.

Equally, you can go back and revisit the radio frequency propagation conditions during any previous time window. Running a WSPR beacon from your home allows you to ‘watch’ the propagation paths open, peak, and close each day under the influences of solar radiation, sunspots, and other ionospheric conditions. Arduinos and a few common accessory boards that can be had for tens of dollars make a beacon accessible to just about any experimenter (with an amateur radio license).

I’m late to the WSPR party. I’ve wanted to try a beacon project for a few years. A while back, I took a copy of the ZachTeck script and experimented with it and a Ublox GPS, but after getting the NMEA strings decoded from the GPS unit at roughly one second intervals, the rest of my code was over-engineered and bloated, and did not fit into the small memory constraints of the Arduino Nano. I put is aside.

Recently, I did a much needed upgrade to my Arduino IDE and libraries. The thought occurred to me that improvements to both IDE and libraries may give me a fighting chance of getting that old WSPR script fitting. When I opened it up, and started to work through it, I saw some obvious ways of reducing memory usage. I had too many String objects (memory-hungry). And my code was writrten to parse each NMEA message string and tokenise it. This allowed me to get to discrete data fields a long way down the messages, like the number of detected satellites. In a simple WSPR beacon, all you really need is the UTC timestamp at the very start of a number of the NMEA messages. I ditched the superfluous stuff and got it uploading, and more to the point, not hanging!

WSPR dataset applications

WSPR is brilliant for teaching you about rare and exotic places that you feel compelled to Google when they turn up on your map in the morning, places like Orlygshafnarvegur (TF4AH, Iceland) or Fuerteventura (EA8BFK on the Canary Islands).

The database of historical propagation across the HF spectrum is widely used by amateur researchers to learn about propagation and has some more serious applications as well. Experimenters have used the data to support ideas or research questions about how symmetrical propagation is at opposite sides of the globe in the same period, and to test antennas. More seriously, a theory was proposed that impressions in the WSPR dataset may indicate the path of the lost flight, Malaysian Airlines flight MH370.

Script

The script is here: https://github.com/prt459/WSPR_GPS_Beacon

Schematic

The schematic is so simple it really doesn’t need a kicad. The Ublox 6M GPS connects to Arduino D2 and D3 for serial data transfer. It also needs GND and +5V. The si5351 breakout board uses I2C and so goes to Arduino A4 (SDA) and A5 (SCK). Connect the si5351’s CLK0 to whatever low power HF amp you like. Mine is from Experimental Methods in RF Design (EMRFD), Fig 12.32, but I could have chosen any number of similar two-transistor stages.

WSPR works on truly tiny power levels. If you connect the bare si5351 clock output to an antenna, you will get decodes! (You should add a Low Pass Filter if this is anything more than a quick test). So use a single 2N3904, or anything with gain, up to a full 5 watt QRP PA with an IRF510 or Mitsubishi RF FET, which is a ‘big gun’ in the WSPR world. Mine uses a 2N3904 and 2N4427 in common emitter feedback configuration, delivering around 10 volts peak to peak into 50 ohms, followed by a W3NQN Low Pass Filter for the band of interest.

Gallery

Acknowledgements

Thanks to Harry from ZachTek for making his code open source. And to Jason Milldrum NT7s for his si5351 and JTEncode libraries.

SPRAT #192

After publication of this project in the RSGBs SPRAT #192 Autumn 2022 a number of builders commented below the post or contacted me with build reports and questions.

First, the 12v DC series decoupling resistor was not labeled in the published schematic, it can be anything between 47 and 100 ohms (see corrected scheatic below).  

Secondly, Ian McCrum did an LTSpice model of the PA which revealed that I omitted  a resistor from the original design in EMRFD (in parallel with the 100n coupling capacitor between the stages) which forms part of the biasing of the PA transistor. If omitted, the PA works, but with reduced power.  Adding the resistor increases the RF power output to around 0.5W, although this will vary depending on drive level, the PA transistor, and the DC supply voltage. Thanks Ian for taking the time to LTSpice this QRP PA.
 
Steve K8SDK got more power out of his PA by increasing the si5351 drive level from 2MA (my value) to 4, 6 or 8MA.  There is a general understanding and some analyses that report the si5351 clock phase noise gets dirtier as you go up in drive level, and for this reason I left it at 2MA.  But with sub 1 watt power levels and a LPF on the output I don’t think it would make any practical difference.

On the question of WSPR beacon power, I don’t think 0.5W is preferable to 0.2W under curent band conditions. With 0.2W the decodes at DX WSPR receivers get marginal and the spread of the band opening can be seen as the grey line moves across the globe. Higher beacon powers can result in saturation which looks like a more rapid ‘lighting-up’ of the remote receivers on the map, and the subtleties of propagation can be lost. This is another way of saying that you should really use a minimum power necessary to get decodes at the far end. However my preference for low power is a personal preference, and some may need slightly higher power to overcome antenna losses.

Several people reporting having to use the set_correction() call with the second parameter (around line 320). I added a comment note immediately above the call in question:

// NOTE: There was a library change to the signature of this method. If you get a compiler error, try this:
// si5351.set_correction(19100, SI5351_PLL_INPUT_XO);

I did it this way to allow for compatibility with subsequent versions of the NT7S si5351 library. But a few people got the compile error and did not trace it back to the offending source line, or perhaps read the comment. I should have just made this change in the repo code to make it foolproof for all comers.

Neil G0ORG emailed with a question about si5351 calibration, his calibration attempt resulted in a value of 149850 for the call to set_correction().  I personally have not seen a calibration offset that large, however, the tiny crystals on the Adafuit and clone breakout boards must vary considerably. Neil reported that this offset pulled his si5351 outside the WSPR passband — we are not sure what went wrong with the usual calibration process for this to happen, bit Neil got his beacon back on the spot by experimentally reducing this large offset value.

Stephen G3ZNG had problems compiling the sketch, and after a bit of investigation discovered he had a previously installed JTEncode library. Upgrading the library fixed the problems and Stephen reported his beacon was working.

Chris G4BMW had the same problem. When he installed JTEncode v1.3.1 and Si5352 v2.1.4 it worked. Chris then discovered that GPS units do not always work inside, and had to move his unit next to a window to give the GPS receiver a sniff of the overhead statellite’s signals.

John G8CHP emailed me a photo of his completed WSPR beacon in a sandwich box. John reports spots in western Canada from his QTH on the east coast of the UK. John used a QRP Labs QLG1 GPS unit, mainly because it was on hand, and a 2N3866 for the PA.

Jonathan G5LUX got his beacon working on a breadboard, and it worked first time.

Aaron K5ATG emailed to discuss his build options, saying that most commercial WSPR beacon products are reasonably pricey for what they are, and my design is made from just a handful of commonly available components, most of which he already had.

Nigel, G4ZA emailed me to say that he had also come up with his own homebrew WSPR beacon, and that Harry’s code (Zachtek) saved him a ton of work too.

Steve K8SDK used three FETs (presumably in the conventional Class E PA configuration as used in many QRP CW PAs) (see comments below post).

And finally, Dave AA7EE has done a superlative job of building his own WSPR beacon using my script, and of course, his blog write-up is amusing, informative and a celebration of the finest amateur radio homebrew spirit. Dave set up his beacon on 10m but had si5351 stability issues which he describes in detail. He solved the drift problems with patience and experimentation, eventually settling on 20m. His post shows remarkable QRPp WSPR results. Thanks Dave for the acknowledgments peppered throughout your post. (See also Dave’s comments below).

A number of builders commented below the post, please read for further discussion. As well, I did receive other emails so if I have missed you please leave a comment below.

My radio projects have involved a build and test effort, often spanning 3, 4 or even 6 months, culminating in one long, detailed blog post which was assembled over many months and a video that serves the dual purposes of showing and explaining the rig followed by an outing to one or more SOTA summits.

One consequence of this is that my video and blog output is quite low. Another is the resulting content is long, detailed, and not necessarily accessible to all readers or viewers. The concept/plan/build/test/box up and, finally, demonstrate approach is akin to building a house over a few years and publishing your account upon completion. So much of the story goes untold — old school thinking in 2021.

Concept

I decided to turn this approach around, in the style of Charlie Morris ZL2CTM who (when in homebrewing mode) pumps out an interesting video at least once a week, in which he shares his thoughts, turns over components in his fingers, sketches out circuits and stages, and involves you in a construction story. In fact Charlie went further and invited his subscribers to suggest or vote on candidate projects, which introduces the risk that he will end up with a project that doesn’t work, a situation which I note Charlie is too smart to have fallen in to.

By opening up a homebrew project, or at least by documenting it stage by stage, taking and incorporating feedback along the way, your viewers come on the journey with you, and the outcome emerges as being kind of our achievement rather than my achievement.

There is also a sense that you (the maker) are your viewer’s surrogate maker, which is a worthy thing, given so many would-be makers lack the time, space, experience, tools, eyesight, dexterity, or freedom to complete a homebrew radio project.

Feeding the YouTube video-monster

There is another reason for taking this approach. After a few years on YouTube I started wanting to know more about how the platform works. Or, how to work it. The motivation to ‘catch more subscribers’ is a thought exercise in itself and I won’t go further on it, as it is different for everyone. Suffice to say that when you go to the trouble of making what you think is a good YT video, you naturally want it to be seen by as many people as possible. That in itself seems logical, human, and not crazily narcissistic.

Guidance on catching more YouTube eyeballs is not difficult to find. Useful clues can be found the videos released by YT themselves to creators. Anyone can view these, and there are no secrets, similar advice can be found on many of the thousands of ‘grow your YT channel’ channels. It basically comes down to a bit of commonsense YT Search Engine Optimisation hygiene, and, mixing it up a bit and keeping on with it until you find your niche, then being consistent. Good and engaging content is king (as if we needed to be told that).

One algorithm input is sustained views. How do you get views? Well, you could mine internet memes, or film yourself doing something totally ridiculous or crazy, or take your clothes off, or annoy Police. The options are endless and most have been tried. Almost nobody watches the same great video every day for a month, so the answer isn’t in making a small number of great videos and expecting them to be watched repeatedly.

The majority of YT creators churn out content as best they can, on a regular basis, typically weekly. And new videos get watched, even if only for a few minutes, generating views, and feeding the voracious YT video monster. Video is a consumable medium. The strategy then is to turn out a good video weekly. With all this in mind I resolved to make a video series about the design and construction of a simple but useful QRP CW transceiver, almost as a byproduct. This post kicks off episode 1 and the 8 part series. The complete transceiver design and build story will be published on YouTube as follows:

Part 1 – Concept
Part 2 – Receiver PCB
Part 3 – Receiver Band Pass Filters
Part 4 – Receiver build & test
Part 5 – Tx PCB, keying, pre-driver, LPFs
Part 6 – Transmitter driver
Part 7 – Transmitter PA and tests
Part 8 – Case, finishing and field test.

Other videos on the rig on SOTA and park outings will be added as they occur.

Promoting solder-melting

The other motivation is to share and promote making, or ‘melting solder’. While blogs are an important record and are critical to convey detail, a picture paints a thousand words and moving pictures moreso. The most powerful, pervasive and pervasive medium is undoubtedly video via YouTube, which has become the world’s goto source for content, how-to’s, and entertainment. And in the best of content, all of these elements come together. So, like it or not, video/YT is now the pre-eminent platform for reaching eyeballs at scale, regardless of content type.

Dual-band 2 channel QRP CW transceiver

‘SP-2B2C’ is a project to design, build and document in a video series the design and construction of a two band (40 and 20m) crystal locked (channelised) QRP CW transceiver. The rig is entirely scratch-built, from ‘borrowed’ designs, circuit elements and ideas. It is a compact, neat pocket rig that will provide more than adequate service as a simple parks and portable rig, but it comes into its own for SOTA where the crystal-locked channels will not be a major impediment to making contacts.

Frequency control is provided by separate dedicated and trimmed 7MHz and 14MHz crystal oscillators with buffers and with a fixed transmit offset. The receiver is a conventional Direct Conversion design with strong band pass filtering and an SA612 mixer, followed by a dual op amp for audio filtering and gain, and an LM386 for headphone or speaker listening. It has ample gain both in the shack and on a windy summit.

The transmitter duplicates a parts of the popular QCX and MTR radios using a high speed logic gate as a digital driver, to three BS170 FETs in parallel for a full 5 watts on both bands. Keying for a straight key is done using discrete components. The receiver draws about 50mA and the transmitter up to 0.8A on key down. Band switching is done with two miniature telecom relays.

Schematic

Case

The aluminium sheet and angle case was made to closely match that of a previous rig, SP-X. I wanted these two rigs to look like big brother and little brother. The 2B2C case measures 52mm wide, 105mm long and 32mm high. That’s 2 inches wide, 4 1/4 inches long, and 1 1/4 inches high.

Critique

The videos have plenty of on-air snippets so it is easy to get a sense of performance. They openly address the design and build challenges encountered so I won’t repeat them here, other than to note a few observations on the design that the astute or experienced viewer will notice.

The first is the 40m receiver note — some of the callers come back at around 300 to 500Hz, not the 700Hz that is usual. This is because the transmit offset is done by pulling the crystal low with a diode switched capacitor (around 22pF on 40m). There is also a series C for trimming the crystal (30pF) to the desired frequency, and these two Cs interact. As this trimmer is closed to pull the crystal down, the transmit offset reduces due to the diminishing effect of the 22pF capacitor. The best compromise I could get was to have the oscillator on 7022.3kHz which delivers around 4 to 500Hz transmit pull.

7022.3kHz is an odd frequency. If the caller nets exactly, they sound a 500Hz note. But I suspect some operators call on 7022, and some on 7022.5, so the caller’s CW note is unpredictable. A solution is to go on eBay and buy two 7023 crystals, and parallel these for (hopefully) more swing, and also, a bit more transmit pull. I might do that, because it would be much better to transmit on 7023.0, not 7022.3, and callers should respond consistently on the whole kHz.

The other obvious limitation is the DC receiver bandwidth, which is probably as much as 8kHz wide. That means strong signals can capture the receiver anywhere in this range. The best QSOs are had on a clear band. The crystal-clear tinkling sound of CW on a DC receiver is a delightful thing, but it wears thin in a crowded band.

Apart from these points I am happy with the usability and performance of this simple CW rig, and look forward to trying it on a SOTA activation soon, once COVID lockdowns are lifted, where I think it will shine!

Acknowledgments

Thanks go to the authors/designers of the various receiver/transmitter circuit blocks I have copied, in particular, Steve Webber KD1JV, creator of the MTR series, and Hans Summers G0UPL whose QCX is an ongoing inspiration. I’ve used KD1JV bandpass filters, and the same RF driver and PA as is in both these designs.

The keying is from RSGB Homebrew columnist Eamon EI9GQ.

Inspiration is drawn constantly from Hayward, Campbell and Larkins’ Expermiental Methods in RF Design (EMRFD).

Finally the SOTA crowd is a global source of genuine interest and know-how in low power portable radios and their operation, and continues the fine amateur radio tradition of operating minimal QRP radios from the mountains and the fields.

From EMRFD.

Cycle 25 postscript

2B2C was built in winter 2021, during long COVID lockdowns. After lockdowns eased it didn’t get much further use, but was carried on some outings as a ‘spare’ rig. Fast forward to July 2023 when I had the opportunity to activate SOTA summit Camels Hump VK3/VC-040 (near Mt Macedon, north east of Melbourne) with David VK3KR.

I took 2B2C, a tiny 3S 1.3AH LiPo, and a 10m wire that I use alternately as a 20m EFHW and a 1/4 wave vertical on 40m. I used one side of my paddle as a crude straight key. I worked 40m CW with fair to good reports coming back from VK2, 3, 4 and 5s.  Around 4pm local time I spotted on 20m and immediately worked a string of DX: ZL1TM, F4WBN, KG5CIK, EA2BD (also running just 5 watts to an EFHW), M0TTQ, ON7PQ, F6CEL, and EA4R. This followup email was receibed from Ignatio EA2BD:

“I was astonished to hear you as I am on holidays visiting some relatives and I just put my wire EFWH antenna on the backyard and connected my Sota gear, a KX3. I’m lucky that this is a noise free environment in the countryside. When I saw your spot and switched on the radio I found 14060 occupied by a EU qrp station calling, but after some minutes I heard another signal slightly off frequency.
I paid attention and… I couldn’t believe I heard you calling. I’m running my rig on batteries and they are a bit flat, so I set to 5 watts and tried calling you for several times. You asked for EA2? and I jumped on my seat!!! Thanks for the QSO, you made my day working with my limited setup. Your signal was solid 429, no drifting and good tone. I was delighted with your straight keying, congrats, you just sounded great!”

At last, 2B2C demonstrated its utility as a basic two-band two-channel CW activator’s appliance. With Cycle 25 doing the ‘heavy lifting’, the possibility of talking half way around the world, even when the other operator is also using the same tiny power level and just a piece of wire, was proven. Bravo QRP!

This AM solid state Class D single band transmitter was assembled over a three year period. Started in 2018, it’s first configuration used a 100 watt push pull RF module published by Drew Diamond VK3XU in Amateur Radio magazine, modulated by a 200 watt linear power amplifier driving a reversed mains transformer, available as a kit from local supplier Jaycar. I built up the RF board, 50 volt power supply (using a stock 300VA toroids mains transformer, no regulator) and proceeded to destroy half a dozen power FETs (STW20NM50) in the RF power stage. Realising I didn’t really know what I was doing, I wisely put it aside.

Not long after I connected with Laurie VK3SJ and Wayne VK3ALK, who coached me along the twisty path of switching technologies for RF, power and modulation– class D H-bridge topologies, 300 watt buck regulators, and Pulse Width Modulators. I quickly learned that switching technology was dramatically smaller, lighter, and more efficient than old school linear approaches. Two homebrew 200 watt transmitters followed, as well as various built and tested AM transmitter modules. For most of this period the 7MHz band had been in the sunspot doldrums, but in 2021 a pulse returned, and so did VK AM stations on 7125kHz. The time had come to finish this project.

The transmitter is comprised of the following modules/PCBs:

• A 300 watt 0..100 V DC linear power supply, consisting of the original toroid mains transformer with an additional hand-threaded 50 VAC winding, a 50A rectifier block, 9,000uF 250v capacitor bank, and a buck regulator to provide continuously variable power from 0 to 100VDC
• Two regulated linear 12V DC 1 amp supplies
• A digital VFO comprised of an Arduino Nano, 16×2 Liquid Crystal Display, various transmit sequencing lines and si5351 triple multisynth PLL
• A Pulse Width Modulator using a crystal clock divided down for 125kHz sampling, IR2110 gate driver, IRFP260s in push pull, followed by a four pole Low Pass Filter with hand-wound RM10 inductors, delivering the modulated DC supply to the RF module
• A Class D H-Bridge PA using a single IXDD614 gate driver and four FETs delivering up to 120 watts carrier
• A 7MHz Low Pass Filter using T106-2 toroids and 1kV glass mica capacitors
• An unbalanced high input impedance microphone amplifier using an audio JFET and a TL071.

Cabinetry, socketry

A transmitter like this involves mains power, and many kilograms of metal and copper. Physical rigidity and having everything bolted down is paramount. I considered repurposing several surplus rack boxes and settled on my favourite, a nice aluminium 3U number, formerly some kind of video switch, that I picked up from Rockby disposals a few years ago. Most of these disposal rack boxes are steel which is difficult for an amateur metalworker like me to drill or file. So if you see an aluminium one like this… grab it. As a bonus, this box included a 240V IEC mains socket and two nice side mounted fans. It also had a front panel bevelled cutout that was cut for a 16×2 LCD, including welded-on mounting risers for the popular 1602 LCDs — perfect!

I left the original labels on the front panel, for provenance, and because they did not annoy me. I cut out the middle centre rectangular hole and backfilled it with 1.5mm aluminium plate, sprayed matt black and labelled. Coincidentally, The new white DecaDry labels I had on hand matched the original labeling nicely. White DecaDry label sheets are almost impossuble to get these days.

Power supply

The power supply consists of a 300VA toroidal mains transformer with 40-0-40 secondary; I wound on another 20V AC winding to get a series total of 100VAC, as well as another 45 turns for 15VAC for 12 and 5VDC regulated supplies. So as not to load down one of these with the in-built fans I added a fourth winding (26 turns for 8VAC), rectified and regulated (via two 7805s), just for the fans. As it all worked out, these fans were not required, due to the 90% efficiency of the modulator and RF board!

I’d never threaded enameled copper wire through a power toroid before. The trick is to use a bobbin as per traditional hand weaving.

Switching regulator

A switchmode voltage regulator (buck converter) regulates the 120V DC HT down to 0 to 100V DC, continuously variable, also performing current limiting and a high SWR cut-out control. The PWM heart of the module is a TL598C PWM controller, with a variable duty cycle pulse train at 120kHz. This drives an IR2110 low side gate driver to a switching FET, that swings the HT across a 120uH inductor and 470uF low-ESR capacitor. A low-value series shunt resistor is monitored by a transistor that turns on at a threshold voltage drop, backing off the PWM controller’s duty cycle. This regulator is identical to that used in my 200W AM transmitter project. For a schematic and PCB (designed later) see Module #2 on this page.

VFO/Controller

I opted for my Arduino Nano/si5351 VFO/Controller. Happily, the original rack chassis had sported a 16×2 LCD and so a perfectly cut and beveled slot and mounting posts were there for the taking. I built a Nano/si5351 and 16×2 LCD to the Raduino circuit on a custom board to fit the front panel cut out and posts. Being that this rig was not a superhet transmitter, I adjusted my script to output a VFO at the signal frequency (7MHz) in transmit (not with the usual IF offset). My script is here. #define SS_VK3SJ_40AM_TX at line 51 to pull in the right code for this project.

The Arduino Nano controls:

• LCD control and data lines
• PTT sensing
• T/R relay control
• Transmitter enable line, which enables the modulator to place DC HT onto the H-bridge PA
• Receiver muting.

I decided to omit any software and hardware for reading RF power (as the PA voltage and current are displayed on front panel meters) and SWR, given the base station antennas always have these inline, and I did not want to over-complicate this build when it had streatched out so long.

Mic amp

The microphone preamp, a 2N5484 FET and TL071, was made up on a small etched board and mounted in its own screened box, including the microphone gain potentiometer, all fitting snugly onto the front panel. This one-off assembly avoided the need for long screened audio cables between the board and front panel. There are no tone controls, this module may be replaced with a more sophisticated mic amp paired with a preferred microphone type.

Pulse Width Modulator

This module takes an HT supply in the range 0..100 volts DC, and line level audio, generates a modulated pulse stream at the chosen Pulse Duration Modulation frequency, and performs power switching into a low pass filter. The result is a modulated DC voltage, suitable for powering an H-Bridge module to generate high quality Amplitude Modulation.

The clock is a 4060 clock/divider that divides an 8MHz crystal down to a 125kHz clock. This clock pulse is transformed into a ramp wave by a Miller Integrator, and fed to one input of an LM311 linear comparator, with line level audio on the other input. The result is an audio modulated pulse stream at 125kHz. This drives both high and low sides of an IR2110 gate driver, then a pair of IRFP260s in push pull, followed by a four pole Low Pass Filter with hand-wound RM10 inductors to effectively convert the PWM into a varying DC voltage (the modulated DC supply) to the RF module.

After assembly and initial testing of the 12v circuitry, the LPF output was connected to a 10 to 16 ohm dummy load. The modulator’s low pass filter has been designed for a load impedance that matches that of the H-Bridge module. As well as following the original designer’s values, I modeled the PWM LPF using SVC Filter Designer from Tonne Software to check the cutoff frequency (28kHz), and input and output impedances.

This module is sized to power and fully modulate up to two of the H-Bridge modules (module #5). This modulator is identical to that used in my 200W AM transmitter project.

RF Power

This module is an H-Bridge class D switch, not a power amplifier in the pure sense as it is non-linear, rather a switching module capable of delivering over 100 watts of power into a 50 ohm load, or other loads with a different output transformer turns/impedance ratios.

For the four FETs you could try Infineon IRFP4019, aimed at class D audio amplifiers, available and priced a few dollars each. I used a better device, the IPP530N15 (was out of stock globally for many months, check supply!). The IPP530N15s have a lower gate capacitance and also a lower drain source on-resistance (Rds) which improves efficiency. The module includes a gate driver (IXDD614, still available), which can be driven with a 5V TTL square wave from a crystal oscilator, synthesiser or PLL (followed by a 74HC-series TTL buffer or equivalent). I have had excellent results wit this driver and FET pairing, with efficiencies of around 90% from 1.8 to 7MHz.

This H-Bridge is identical to that used in my 200W AM transmitter project (which used a pair driving a W8JI RF power combiner). For a schematic and PCB (designed later) see Module #5 on this page.

7MHz Low Pass Filter

The LPF is a conventional W3NQN design. I used T106-6 toroids and 1.2mm enameled copper wire, probably capable of a kilowatt. The capacitors are beautiful 1kV glass mica pieces, quite pricey but essential. I tried what I thought were decent quality 1kV ceramics at one point, and they got worryingly hot! My local supplier for these glass mica pieces is PKLoops, you will need to email them for a current stock list, check out their other products as well.

Comments

Testing and final alignment was done one module at a time. The safest approach with the power switching modules (Regulator, PWM, H-Bridge) is to bring up the 12V section and validate correct operation, then apply HT at around 10V with an appropriate load attached, apply drive, and carefully monitor the gate and drain waveforms.

In general, these circuits have mostly been easy to get going, and stable. A few FETs were blown up in the H-Bridge when operating at around 100 watts or more, mostly due to ragged looking drive waveforms across the gates. It is fairly much essential that you use a current limited DC HT supply — to test and put these H-Bridge modules on air withour current limiting is tempting fate. The Regulator module includes this feature.

With switching circuitry, most of my problems seem to have traced back to improper gate drive waveforms. When the drive looks good, you can turn up the HT to the switching FETs and there should be an almost linear increase in the output waveform amplitude. This is particularly impressive on the H-Bridge, where you see the board deliver 5 watts on a 8 to 10V HT, then up to 120 watts as the DC rail approaches 80 to 90 volts (depending on the load impedance presented by the output transformer’s primary at the frequency of interest).

The H-Bridge’s IXDD614 low side gate driver can draw 600 to 800mA on a 12V DC supply. It has been worth reducing the supply down to 10V, 9V and even 8V whilst monitoring the H-bridge’s output waveform. Most times, the output square-ish wave maintains its shape when the driver’s supply is reduced, which allows the IXDD device to run a lot cooler.

Another protection mechanism for modules permanently installed in an AM transmitter is SWR protection. An SWR bridge and detection unit can be used to detect high SWR and kill the PWM board (thereby dropping the HT to the H-Bridge) in the presence of high SWR. The one I used in another transmitter is module 3 here.

I have not included a complete schematic for this project as is my usual practice, as all of modules are described in other posts and pages. As noted, the H-Bridge, Pulse Width Modulator and 100VDC Regulator are each described on the AM Modules page, with schematic diagrams and some build notes.

Leave a comment below if you want to scratch build any of these. I can share prototype PCB Gerbers if you wish, but these are my own first version prototypes, and I cannot guarantee these are not without minor issues. If you try any of these modules yourself, let me know how it goes.

Acknowledgements

Thanks to Laurie VK3SJ and Wayne VK3ALK for guiding me in understanding and reproducing these modules over several years.

Build notes

Secondary winding 2: 68 turns gave 24VAC (0.353 volts AC/turn); therefore 127 turns should give 45VAC.
Secondary winding 3: 15VAC == 43 turns
Secondary winding 4: 8VAC == 23 turns.

I’ve long been interested in compact and fairly minimal SSB and CW rigs with good performance. I’m not into bells, whistles or menus. Menus are for restaurants! When hiking, walking or bouncing around summits I want to minimise things that are not absolutely necessary, things that can go wrong. Less is more when it comes to a transceiver for portable work.

The first place to reduce unnecessary complexity is your mode. In Australia, a number in the SOTA crowd have slowly adopted CW as the mode of choice . This makes sense for operating QRP with sometimes compromised antennas. The CW trend has been assis ted by increasing and enthusiastic bunch of ZL activators who appear to use CW almost exclusively.

In recent activations it has been common to spot on 20m CW and be rewarded with 3 to 5 ZL chasers, all reliable reports between s3 and s5. Then, a spot for 40m CW should bring forth equal numbers of ZL and VKs. CW exchanges are formulaic, businress-like transactions with 73 GL and dit dits to conclude. No long social obligations concerning handle, rig, wx. A CW activation is efficient and fast. You can bag 7 or 8 chasers in minutes. Reducing your qualifying time let’s you keep moving, or, gives you more time to enjoy the mountain top experience.

There’s another noteworthy feature of CW activations. They nearly always use the same frequency. 7032, 14062 kHz. And on a SOTA activation, the standard procedure is that you spot with one of the apps, call CQ SOTA, and the chasers line up to work you. You hardly ever touch the dial. In fact, you hardly even need a tuning dial !

That got me thinking. How minimal could a CW multiband rig get? In a dedicated SOTA CW rig, do you really need to be able to tune around the band, or could you get by with fixed ‘channels’?

Concept

The concept for this project is that of a CW ‘appliance ‘, a device that you pull out of your pocket, plug in the antenna and paddle, choose your channel (aka band) and hit the keyer button to send CQ and get the activation started. The appliance would need to cover at least 40 and 20m, the two VK/ZK SOTA CW watering holes, and one or two additional higher HF bands, where short antennas offer interesting variety as Cycle 25 rises.

Five watts should be plenty. An inbuilt top-facing speaker with a headphone jack will suit all listening situations. Small and light goes without saying, as does the option to operate on an external 3S or 4S LiPo pack, possibly even strapping the battery to the rig.

It will need to be physically sturdy without being too heavy — 3 to 400 grams seems like a good target weight.

Choices

A simple, dedicated CW rig shouldn’t require a complicated receiver. A single conversion superhet is in order. I studied various designs by Steve Weber KD1JV, particularly his MTR5B and SodaPop. The Mountain Topper range are very well regarded, even romanticized by some owners. The MTR5B is a dual SA612 receiver with 4.915kHz IF. The more recent SodaPop uses a pair of JFETs in each mixer, but is otherwise similar. I also looked at the receiver in the Elecraft K1, also an SA612 design.

I’m a fan of the SA612, with a decent bandpass filter and a resonant antenna ahead, proper impedance matching and a bit of extra IF gain downstream. I have not had any problems with these receivers with basic but decent antennas on mountains or at home. What some northern hemisphere hams do not realise is that the bands in VK and ZL are more or less empty when compared to what we see on USA and Euro SDRs. Pull up a session on 80 or 40 anytime on my local receiver and see what I mean. Also, VK hams are capped at 400 watts which eliminates the ‘kilowatt around the corner’ problem we hear talked about. And our lower population density limits the Broadcast breakthrough suffered by some who live in densely populated areas. So we are lucky here, living in a region with a low density of hams, although it has its drawbacks as well.

I also looked at receivers using diode ring mixers such as the Bitx, but these receivers require higher oscillator injection levels that necessitate non trivial buffering and level setting over the rig’s intended frequency range. Gilbert Cell mixers have useful conversion gain and avoid this complexity to some degree.

I also looked at the QCX, which uses a higher performance quadrature detector. It’s an option in a compact and portable analogue receiver if you use Hans’ polyphase kit to do the audio phase shifting for a single signal audio output. Also the mixer requires a 4x VFO as input to the usual 74AC74 divider, not really a problem with an si5351 but I’ve not tried it before.

The best path to realising one of these would be to buy Hans’ High Performance Receiver and Polyphase plugin kits. The resulting assembly is only 80mm x 50mm, so with a VFO (no BFO necessary because it’s base-band) there are some good options for a partially scratch built multiband version of the QCX. Interesting. I’ll leave that concept for another time.

Schematics

Page 1 is the transceiver core:

Page 2 is the Arduino Nano, si5351 and controls:

Construction

Construction methods followed my established combination of stacked (hand-drawn and etched) PCBs housed in an aluminium sheet and angle case. The transceiver was designed as two self contained modules, the VFO/BFO and Controller (Arduino Nano and si5351), and a second housing receiver, BPFs, transmitter and LPFs.

VFO/BFO/Controller

This module was designed and built first. It followed the common pattern of an Arduino Nano, si5351 breakout board, 78-series voltage regulators, a discrete clock buffer on the CW clock (CLK0), sidetone filtering and some switching components. The module consists of two PCBs — a single sided hand-made base board is bolted flat against the aluminium base plate with side controls mounted directly on the board. Front panel controls are mounted against a double-sided hidden front panel PCB with perpendicular bracing pieces. Two 8-pin 0.1 inch DIL header sockets at either end support the daughterboard on top which houses the Nano and some logic.

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A vertical line of three miniature pushbuttons at the left hand end of the front panel implements the transceiver’s frequency control. The middle button is the channel button — push it, and you move to the next channel. A channel is a semi-fixed frequency in one of the four supported bands — 40, 30, 20 and 17m. Each of the six channels has its own LED on the front panel. The mapping of a channel to a band and frequency is fixed in the firmware (but is easy to change).

The upper and lower buttons ‘bump’ the channel (VFO) frequency up or down by 100Hz. So to move 1kHz from the default channel frequency, you need to pump one of these buttons ten times, counting as you go. After a few seconds, the current frequency is written to EEPROM and will persist over a power-down.

So, if you have ‘tuned’ the rig away from a channel (such as 7032kHz, the 40m SOTA CW calling frequency) how do you get it back? Easy! You hold down the channel button for a second and it reverts to the hard-coded frequency. If you wish to change any of the channel frequencies, you edit the Arduino script and upload it to the Nano, whose USB is accessible through a slot cut into the transceiver’s left side panel.

Receiver and Transmitter module

This module uses an upper and lower PCB pair, with transmitter on the bottom and receiver on top. In a departure from my usual T/R relay to switch antenna and DC power, both are done electronically. In fact the receiver is permanently on, so there is no need for a separate +12 volts (receive) line. The RF switching arrangement is copied straight from Steve Weber’s MTR5b, and is almost the same as is used in the QRPLabs QCX.

Receiver

The receiver is a standard superhet with SA612 Gilbert Cell receive mixer and product detector and a 5 pole homebrew crystal filter. The design is almost identical to VK2DOB’s MST3, and KD1JV’s MTR5B (which doesn’t have the additional IF amp stage). I built my crystal filter at 4MHz but only because I didnt have any 4.915MHz low profile crystals in the junk box. My filter exhibits steep skirts and a bandwidth of about 300 Hz. Just about right for CW.

I added an additional gain stage after the mixer which makes a difference to receiver liveliness, remebering that the 5 pole narrow crystal filter is a point of significant attenuation.

Band Pass Filters

In previous projects I have strictly adhered to tight bandpass filters, one per band, and always using hand wound inductors on T37 or T50 toroids. Favourite filter designs have been those of Eamon EI9GQ from RSGB RadCom, and Diz W8DIZ of kitsandparts.com, both easily reproduced filters. This time I tried something different — a different filter design using electronic switching and surface mount inductors.

The filters are taken from the hardware portion of the RS-HFIQ project, a modern baseband SDR. They are much broader in bandwidth than I’ve used in the past, as the sweeps show. This means that the Gilbert Cell SA612 receiver mixer will be exposed to more out of band RF energy coming down the antenna, which could result in overload. Let’s see.

The filters are electronically switched using a 2N7002 FET between the filter earthy end and real ground. Pin diodes (from Minikits) do the switching. This saves a relay and relay driver.

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CW transmitter

The transmitter portion reproduces those of Steve Weber’s MTR-5B and SodaPop as well as Hans Summers’ QCX, and uses three BS170 JFETs in parallel driven by a high speed logic gate to deliver up to 5 watts of RF to the Low Pass Filters. Once the drive level was padded to ensure at least 4 volts was hitting the BS170 gates, it worked as expected.

This is a Class E switching configuration, so unlike a more conventional Class A or AB RF power stage there is no bias, meaning it draws no current at all between dots and dashes, and is around 90% efficient.

On the bench the transmitter was drawing 300mA at 14V for 3 watts of RF (remember the Digital VFO and Controller draw 80mA). Observant readers may notice that the driver logic gate is a 74HC00 NAND, not the usual 74HC02 NOR, only because the NAND gates were on hand. No drive problems have been observed as a result of this substitution.

Low Pass Filters

Continuing the spirit of simplicity and to save space, two LPFs are used to cover the four bands (40 and 30m, 20 and 17m), a common technique in QRP rigs. These are 7 element W3NQN filters. Remember that a resonant antenna plays a vital part in the transmitting system’s overall spectral purity.

Solid state TR switching

In another break from my past practice of using miniature Telecom relays for transmit/receive switching, the series JFET used in KD1JV’s designs was tried. An almost identical arrangement is used in the QCX. No appreciable received signal loss was experienced, and the JFET appears to be an effective blocker for RF power from the transmitter at the 5 watt level.

Receiver muting

Despite using a solid state analogue switch (TS5A3157) in series with the audio signal path, getting a silent CW break-in switch (from receive to transmit then back again) proved to be a major headache. On my PCB the TS5A3157 switch was inserted between the two op amp audio stages. This resulted in an annoying click going both into and out of transmit. No amount of bypassing or fiddling with signal levels made much difference.

I checked for DC levels around the input of the TDA2003 IC and found a DC offset of about 1.4V on pin 1 (input), which is always blocked with a series 2uF capacitor. Nothing unusual there. I wondered if this series 2uF electrolytic was charging or discharging, bur reducing it to 0.1uF made no difference.

Next, I build a small vertical board with a second 3157 switch, right next to the TDA2003, with just a series 100n capacitor from its output to the volume control, which itself was isolated from DC with 100n capacitors. That made no difference.

It is strange how you can get fixated on things like this. The rig was useable as it was, with what some might call an acceptable click on change-over. But I wanted a noiseless changeover, and the quest turned into a series of experimentation and debugging sessions that stretched far beyond what I’d expected.

I now regard noiseless T/R switching in a CW rig with an audio power stage capable of driving a loudspeaker to be a non-trivial problem. As I was studying the KD1JV (MTR, SodaPop) and G0UPL (QRPLabs/QCX) designs I realised that they both support headphones only, not loudspeakers. Could it be that lower volumes made this problem less pronounced?

The problem is as follows. You want a noiseless transition from CW receive to CW transmit and back again. It has to happen quickly to make even ‘semi-break-in’ work. But in transmit mode, you want the sidetone to come through in your speaker. So you cannot disable or mute the audio power amplifier stage, otherwise you lose the sidetone. As well, you want to have the sidetone come via the volume control, so that turning the volume up or down affects both receiver audio and sidetone.

I reluctantly decided to ditch the solid state audio switch (which was making an annoying click on both transitions) and replace it with a relay at the input of the volume control and audio power amplifier, switching the audio source between receiver noise and sidetone. Mercifully, this resulted in a silent Rx to Tx transition, but, when the transmitter dropped out, a nasty click! This was particularly annoying as I’ve successfully made noiseless TR switching with TDA2003s and a relay in two other rigs.

Finally I added a second relay to mute the audio power amp for a short period (after the last character had been sent and just as the rig reverted from transmit to receive). A second digital control line coming from the Arduino, and some orchestrated timing in software was needed.

Eventually, I achieved silent T/R switching, and it is a pleasure to use. How to mute the audio amplifier’s transmit to receive click more elegantly? If the audio IC I’d chosen had a mute pin, that would suffice. But the TDA2003 is an old car radio audio amplifier and has no mute. So I took the brute force action. Normally closed, this relay opens for a few hundred milliseconds and silences the click from the power amp. This arrangement is shown above for all to see.

Case and finishing

The case measures 70mm wide, 132mm deep and 32mm high, and is made from hand worked aluminum angle and 1.2mm sheet for the base. A top cover is from 1mm sheet.

The front panel is finished with all purpose metal primer, three enamel coats (colour is called ‘aluminum ‘ and is an appealing silver-grey). Lettering is rub-on DecaDry. Two coats of clear satin enamel spray seal the panel. The side panel is labels applied direct to the aluminium angle piece, with a satin clear top coats.

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On the Summits

After a few weeks of bench testing it was time to try the little rig in the field. Two nearby SOTA peaks, Mt Vinegar VK3/VC-005 and Mt Gordon VK3/VN-027 in the Yarra Ranges acted as a proving ground and offered 10 activator points in total. Both are miles from residential areas and offer the chance to play radio in a noise-free environment.

After a 90 minute drive followed by a 90 minute (at times strenuous) walk from Acheron Way up four wheel drive tracks to the summit, we were on-air on Mt Vinegar at around 1.25PM local time. Antenna was a linked dipole for 20 and 40m on a 9m pole. Starting on 20m, two of the regular New Zealand chasers called in, ZL1BYZ and ZL1TM, weak but workable, 539 reports coming back. VK2IO provided a third 20m QSO. Moving to 40m, four chasers (VK2IO again, VK2WP, VK5IS, and VK5HAA) called in with reports ranging from 419 to 559.

The rig performed well as expected, although the audio output level (or receiver gain) on 20m seemed a touch low.

From here we moved on to Mt Gordon VK3/VN-027 on the outskirts of Marysville, a drive-up four pointer with a comms and fire watch tower, and a great view of the Cathedral Ranges to the north. 20m yielded just the one QSO with ZL1BYZ (thanks John, you are amazingly reliable!). A QSY down to 40m caught VK2GAZ, VK5HAA, VK2LI, ZL3MR, and VK2IO again, with all R5 reports ranging in strength from 2 to 5. Now, later in the afternoon (we finished around 5PM), both 20 and 40m were more lively and the receiver correspondingly louder.

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Improvements

Back on the bench a few fixes and improvements were made. The hole on the side panel was widened to stop the CW keyer message button sticking. The single 2N3904 IF amplifier stage, originally using a resistive collector load and a series coupling capacitor into the cyrstal filter, got a 10 turn FT37-43 bifilar transformer on its output which improved its overall gain by some dB. A number of minor firmware changes were made. The top plate was cut and this greatly improved the speaker volume. Never judge an un-baffled loud-speaker.

Size and weight

Comparisons with the tiny and much loved Mountain Toppers are enlightening. The MTR-5b (the inspiration for SP-X) apparently weighs 6.4Oz or 181 grams. That’s light! I believe this is sans batteries. SP-X weight 332 grams, a lot more. About 27g is attributable to the speaker which the MTF-5b doesn’t have.

The MTR-5b is 4.27″L x 3.2″W x 1.34″T. I make that 10.8 x 8.2 x 3.4 cm or 301 cm3. SP-X is 14 x 7 x 3.2 or 313cm3 — about the same volume.

To get the weight (and size) down further, you’d need to ditch the homebrewer/maker-parts (the Arduino Nano and si5351 breakout) and use exlusively surface mount components on a purpose-designed and fabricated PCB. This represents a big step from a prototype like SP-X to a product that can be produced and sold in a run. There are examples all over the crowd funding sites. It’s the logical next step but it requires different skills and it’s not really my game. Kudos to Steve Webber for his achievement!

Closing comments

SP-X, like all my projects, are prototypes without complete revisions and iterations to follow. I’ll never go back and build a second version of SP-X with the workarounds and mistakes corrected. As a consequence I’ll live with a few re-worked stages (such as the receiver muting fix). A more considered solution to the muting problem might involve a comprehensive end to end design of the audio stages from detector to loudspeaker. Perhaps you’d have two digitally controlled potentiometers on the I2C bus to act as faders between the two audio sources and an audio power IC with muting that you knew could be trusted to switch silently. Maybe there is a simpler way of doing this in a rig with a 5 watt audio stage. Feel free to let me know in a comment!

I’m very happy with how this little rig turned out. It is compact, light, useable, simple, and as versatile a portable QRP CW station as I’ll ever need. I’ll be happy to trust it to get me the four QSOs on any VK3 activation in the future. It simplifies and lightens the rest of my load, particularly the battery which is half the weight of its predecessor. If I built it again I’d fix the receiver muting and probably try to accommodate a LPF for each band. Other than that, I’d build it as it is.

And channelised SOTA CW is a breeze — who needs a tuning knob and display anyway?!