Portable antennas (verticals, loaded dipoles) typically use coils on the lower HF bands to make them electrically "larger" to alow them to be resonated at frequencies well below their physical size - but what about losses in those coils?

While it's "traditional" to use copper wire wire for these coils, there are a number of modern offerings that use stainless steel - and both types have their cheerleaders and detractors, so what's the deal?

Figure 1: The JPC-12 vertical in the field.

Note:  This post refers to previous entries on this blog about the JPC-7 and JPC-12 antennas that are relevant to this discussion, namely:

• JPC-7 loaded dipole antenna - link.
• JPC-12 portable vertical antenna - link.
  

While some details in this article are specific to these antennas, the general observations may be applied to any HF antenna using loading coils.  I have not (yet?) done A/B field tests with antennas using different (stainless vs silver plated/copper) coils and/or simulations - perhaps a topic for a future blog entry?

* * * * *

In previous posts I have discussed the JPC-12 vertical and the JPC-7 dipole:  To make either antennas usable at frequencies lower than their natural resonance, inductance is required (the "loaded" part) to achieve resonance at the desired frequency - and for their lowest operating frequency - 40 meters - it takes a fair bit of "loading", indeed.

For this, the JPC-7 dipole, which has a "coil-less" resonance of around 22 MHz, has two coils with adjustable taps - one for each element - a slider being used to adjust the amount of inductance:  Higher inductance = lower frequency.

The JPC-12 vertical - made by the same folks - unsurprisingly uses the exact same coil as the JPC-7 - and for the same reason:  To add inductance to make the electrically-short element - a radiator of approximately 150" (381cm) total length (resonant around 18 MHz without any added inductance and using the originally-supplied components) offer a semblance of a match on lower bands.

Having the coil in common, they also share the same trait:  Loading coils wound with stainless steel - and since, when running on a lower band like 40 meters - all of these coils run quite warm at nominal transmitter power (100 watts or so) there are definitely power losses in the coil - but how bad is it?

Wanting to answer this question, I ordered an extra coil from the seller from which I'd bought my JPC-7 and JPC-12 antennas and with that - and the three that came with the two antennas originally - I now had four coils - enough to do direct A/B comparisons on both antennas when I rewound two of them with silver-plated wire.

Why stainless?

The coils originally supplied with the JPC-7 and JPC-12 are wound with 1mm diameter (18 AWG) stainless-steel wire.  Fortunately, an austenitic (non-magnetic, as checked with a neodymium magnet) type of stainless steel is used:  If this wire been magnetic at all things would be much worse in terms of loss.  While the 1mm diameter stainless steel wire is very rugged physically, the fact that it is stainless steel means that its resistance is quite high compared to copper - in this case the end-to-end DC resistance is about 4 ohms, but the RF resistance, taking the "skin effect" into account, is likely to be very much higher.

Using Owen Duffy's online skin effect calculator (link) and assuming 1mm diameter, 316 Stainless, the 4 ohms of DC resistance translate as follows to RF resistance including skin effect:

• 3.5 MHz = 5.2 ohms
• 7 MHz = 7.2 ohms
• 14 MHz = 9.6 ohms
• 28 MHz = 13.6 ohms

These values would be for the entire coil, but since one uses slightly less than the full number of turns of the coil to resonate at 40 meters, the losses should be lower - but the message is clear:  The less of the coil that you need to use, the lower the loss.   The total length of 1mm wire is estimated to be about 180 inches (457cm) and  by comparison, copper wire of this same diameter and length would have a DC resistance of about 0.1 ohm - or, according to Owen Duffy's calculator, a skin effective resistance of 2 ohms at 28 MHz.

Why stainless steel, then?  Obviously, stainless steel won't oxidize/corrode like many metals - and it may be that in quantity, stainless steel wire is less expensive than silver plated/copper, but in this case I believe that there's another reason.  Other manufacturers of portable antennas (Wolf River, for example) advertise the use of stainless steel for their coils as well, extolling the virtues of the material in regards to its inability to corrode - but I'd be surprised if such corrosion is likely to be the main reason for a hypothetical copper coil's losses in an electrically-short antenna that would make it worse than stainless.

I suspect that the "advantage" of a stainless steel coil is, in fact, related to the fact that it is lossy.  As portable antennas - when used on the lower HF bands - are necessarily smaller than their full-sized counterparts, their radiation resistance will be commensurately lower and this means that the feedpoint resistance may be lower as well when fed with simple matching schemes such as a series coil.

What this means is that rather than somewhere "around" 50 ohms, the feedpoint impedance when using a very low-loss coil may be much lower, resulting in an "unacceptable" VSWR (e.g. >2:1) at resonance:  While this would actually imply greater efficiency due to lower loss, it's "inconvenient" to the user.  While a more versatile means of matching the antenna is possible (multiple coil/capacitors such as a simple antenna tuner or the use of an autotransformer) this complicates construction, operation and can increase cost.

As implied earlier, another method of dealing with low feedpoint impedances is to add series resistance to raise it to something closer to 50 ohms to make radios (and their operators) "happy" - but an ohmic resistance in the signal path (say, the use of stainless steel) means power loss, and power loss means heat!

How hot is it?

Figure 2: The original loading coil (lower) wound with stainless wire as seen with a thermal infrared camera.  After 60 seconds at 75 watts (on 40 meters) the coil temperature rose by 110F (61C) from the ambient 53F (12C) to about 166F (74F)! Click on the image for a larger version.

I've operated both the JPC-7 and JPC-12 antenna a number of times in the field on the "lower" bands of 40 and 30 meters at 100 watts, using both CW and SSB, and observed that in each case, the coil gets "hot".  As the coil forms are (apparently) molded nylon, this is nowhere near the likely softening point of more than 300F (150C) - and being open to the air to allow convective cooling, and using a mode where the duty cycle is intermittent certainly helps prevent a "meltdown".  (Compared this to PVC - which has a softening temperature in the area of 140-180F or 60-80C)

As a test, I put both the original stainless steel and the rewound silver-plated coils in series on the JPC-12 vertical, putting a jumper across the coil not under test.  I then transmitted 75 watts into the JPC-12 vertical for 60 seconds and measured the temperature of the coil with an infrared thermometer and thermal camera, noting a temperature rise of about  110F (61C) - still not hot enough to risk melting the coil form, but certainly enough to dissuade one from running a 100% continuous mode like SSTV, RTTY or other digital modes on a hot day!  (Note:  On a hot day a temperature rise of 110F/61C may well be enough to soften a PVC coil form.)

The picture in Figure 2 - taken with a thermal infrared camera - shows the heat produced when testing with the JPC-12 vertical.  (Note:  During this test I swapped positions of the two coils to see if there was much difference in the current/heat of the stainless coil owing to differences in current distribution, but as expected, there was not.)  Similar results were observed when operating SSB and CW on the JPC-7 loaded dipole.

At this point I should make something clear:  The reader should not presume that the use of a stainless steel coil is going to result in an antenna that doesn't work, but rather it implies a degree of loss of efficiency.  As I've made many contacts with both the JPC-7 and JPC-12 in their original form, I know that it's perfectly capable of usable performance - but how much better would it be if we were to address coil losses?

Also, once I had seen the loss in the coil, I couldn't "un-see" it and I had to do something about it.

Choice of wire

In order to minimize losses in an electrically-small antenna it is important to reduce resistive losses and the loading coil and reducing the generation of heat produced by it is a good place to start - and copper wire is an obvious choice.  Knowing that the wire used is 1mm diameter - about 18 AWG - there were a lot of choices:  I had some enameled 18 AWG wire already on-hand and I could easily have obtained some tinned 18 AWG "buss" wire as well.  Finding bare copper wire was a bit more difficult, but since we need only make contact on the ends and along the slider, there's no reason for the entire coil to be bare and thus be subject to oxidization:  If I needed to do so, I could have wound the coil with enameled wire and then selectively remove the insulation along the path of the inductor's slider with fine sandpaper.

On a hunch, I did a search and quickly found on Amazon some 1mm (18 AWG) "Silver plated" copper wire of the same diameter described as being used for jewelry - a small spool costing about US$15 with more than enough wire to re-do three of these coils. ^{Footnote 1}

Figure 3: The coil - still with the stainless steel wire.  On the left end of the slider (the "top") of the coil can be seen the insulator. Prior to disassembly move the slider to the end opposite the insulator (maximum inductance) as shown.  When removing or installing the Allen screw, keep a firm grip on the end with the insulator to prevent it from rotating and damaging the insulator itself or the end of the rod that protrudes into it. Click on the image for a larger version.

The use of silver-plated wire is traditional in RF devices as it has the advantage over copper wire in that as it oxidizes, the result (e.g. silver tarnish) is still a conductive substance, much better than copper oxide - and compared to bare copper it is less (chemically) reactive overall - plus the coil looks very nice!

Rewinding the coil:

The coil form itself - with molded grooves - is quite rugged and lends itself very well to being rewound by hand.  Using a silver-colored "Sharpie" I noted where the original coil's windings started and ended.  I would also recommend taking a photo of it - particularly if you are rewinding the coil of a JPC-12 vertical and do not have a second coil as a comparison.

It is also important to note that one end of the slider is insulated to prevent the shorting the unused turns of the coil itself - something that would surely reduce "Q" and overall efficiency:  It is important to reinstall the slider assembly in the same orientation as before to put the insulated end of the slider rod on the "top" (e.g. the side closest to the top of the vertical or end of the dipole).

When rewinding, first move the slider to the end farthest away from the end with insulator on the rod (e.g. the "bottom" of the coil, with the stud protruding) and cover the spring contact with a bit of tape to keep it with the slider body:  This moves the slider - and the contact spring - well away from the end of the wire that we are going to remove first.  Using an Allen wrench, carefully remove the screw holding the end of the slider bar with the insulator (e.g. the part at the top of the coil, with the female threads):  The end of the wire is tucked under the supporting post and the screw itself goes into the brass slug at the center of the coil with the M10 threads used to assemble the rest of the antenna.  Keep tension on the hardware with a finger as you undo this to minimize the possibility of it being launched across the room.

Figure 4: This shows the end of the new wire looped around the screw and the post tightened down to hold it in place as it is wound. A blade screwdriver is used to push the wire into the groove below the slider boar to keep it from jumping out of the slot. Be sure to start the wire in the same place as the original coil. Click on the image for a larger version.

At some point, the coil of stainless steel wire will unwind itself rather forcefully when it slips out from under the screw (it may be a good idea to wear glasses) as it is under a fair bit of spring tension:  Even if you are prepared for this to happen, it can be startling!  At this point be sure that the contact spring is still on the slider block:  If it is not, look for and find it now!

With the tension released, remove the other end of the slider bar.  At this point, carefully remove the slider bar from the insulated end so that you have just the support post and set the rest of it aside.  At this point you'll have a loose coil of stainless wire to set aside.

Take the end of the new wire and using a pair of needle-nose pliers, bend a loop to go around the screw for the support post and using (just) the support post that was insulated for the slider, secure it in place, under the post.  Lay the wire in the groove and at the point where you marked the coil to begin, lay the wire in that groove and then push the wire into the shallow slot above which the slider moves to hold it in place.

Figure 5: As the wire is wound, keep pressure on the wire and coil form with a thumb while rotating the form itself, forcing the wire to drop into the molded slots.  Continue winding until you get to where you had previously marked the end of the original coil - but there's no harm if you add one extra turn. Click on the image for a larger version.

Keeping the wire under tension - and using a thumb as necessary to hold that tension and push it onto the form - tightly wind the wire onto the form, making sure that it drops into the wire slots.  When you get to where you marked the end of the coil (you can go one extra turn if you like!) push the wire into the slot again (to help hold it in place) and - leaving enough extra to go around the screw on the bottom of the coil - trim it off.  Before putting a loop in the end of the wire to go around the screw, again use a blade screwdriver to push it into the groove to help hold it into place.

At this point I temporarily wrap a the loose end of the coil with a bit of electrical tape to keep it from unraveling while I loosen the post at the top of the coil and align it carefully so that I can plug the slider bar back in and re-mount it and the other post at the bottom of the coil, torquing the screws firmly and being careful to prevent the post with the insulator from twisting as this is done.

Figure 6: The finishing end of the coil with the wire looped under the slider rod support and tightened down.  In this picture you can see how the wire has been pushed into the groove, under the slider.  To the left of the end of the wire can be seen the blob of adhesive used to lock the end of the coil into place. Click on the image for a larger version.

Now, the coil has been successfully re-wound.  While it may not be strictly necessary, I put a dab of "Shoe Goo" - a thick rubber adhesive - on the top and bottom 2-3 turns of the coil near where the wire drops into the slot and connects to the post to "glue" it into place, making sure that it doesn't jump out of its slot.  If you don't have "Shoe Goo" or something similar, some RTV ("Silicone") can work as can epoxy - but cyanoacrylate and polyurethane glues (e.g. "Super" and "Gorilla" glue, respectively) may not work very well - and "hot melt glue" are definitely not recommended as either will likely break loose their bonds across a wide temperature range and changing mechanical stress. 

The trick here is to bridge several turns of wire with the adhesive to lock them into place together as much as adhere them to the coil form.

Results

Figure 7: The coil rewound with silver-plated wire (upper), under the marker.  As can be seen, the temperature rose by about 3F (less than 2C) above the ambient temperature of 53F (12C) after 60 seconds of key-down on 40 meters at 75 watts. Click on the image for a larger version.

As expected, the use of lower-loss wire for the coil results in a dramatic reduction of generated heat which no doubt corresponds with an improvement in overall antenna efficiency - The "after" picture (Figure 7) of the coil using the thermal camera after 60 seconds of transmission on 40 meters with 75 watts shows the difference.  As in Figure 2, the original stainless steel coil is on the bottom, but it is the one that is jumpered, putting all of the RF energy into the upper (silver-plated) coil, instead.

Touching the coil immediately after the 60 second key-down, the loss-related heating of the coil wound with silver-plated wire was barely perceptible - a far cry from the original stainless-steel wound coil that was  "hot"!

Electrical comparison of the stainless and silver-plated coils

For capacitors and inductors, one measurement of their departure from the ideal is their "Q" (e.g. "Quality Factor") and for inductors, the majority of this is likely to be the radio of the inductive reactance of the coil (X_L) to its ohmic resistance.  I decided to measure the unloaded "Q" (Q_u) of the original stainless steel loading coil and the rewound silver-plated coil.  To do this I used a NanoVNA and the method described in W7ZOI's article "The Two Faces of Q" (link) under the section called "Measuring Resonator Q":  I used both methods (#1 using parallel L/C and #2 with L/C in series) to determine the "Q".

Using method #1, for the "C_c " capacitors I used two 1pF NP0 capacitors in series each (0.5pF) which resulted in a 35-45dB through loss at resonance.  I put a high-quality 27pF silver mica capacitor in parallel with the coil under test and measured the -3dB response of the resonance curve.  In this test I set the variable inductor to the mark indicating tuning for 40 meters (around 22 uH) which, with the 27pF capacitor, yielded a resonance in the area of 6.6 MHz for each of the two coils being tested

Assuming that the Q of the series silver mica capacitor (C_o) is 1000 (a mediocre value - it's probably a bit higher) the results were:

• Original stainless steel coil unloaded Q:  47
• Rewound coil (silver-plated wire) unloaded Q: 199

I then used method #2 (with L/C in series) and got:

• Original stainless steel coil unloaded Q:  47
• Rewound coil (silver-plated wire) unloaded Q: 221

At the risk of being accused of "cherry picking" my results, I'll note that for high "Q" values and where the value of C_o is quite small, method #1 is less forgiving in terms of variances and minor losses in the test fixture, so we'll use the value from method #2.  The reader should also note that with a higher Q, deficiencies in the test measurement and effects of the coil itself will result in lower than actual Q_u (e.g. you will not get an erroneously higher value of Q) so it is likely that even the higher reading from method #2 on the silver-plated coil is, itself, a bit conservative.

Note:  During testing I observed that just laying the coil on my wooden workbench lowered the Q of the silver-plated coil significantly (15-20%) so all readings were taken with both coils held about 12" (25cm) above it.  I think that there is likely some effect of free-space capacitance that is reducing the reading so I suspect that the "actual" Q_u of the silver-plated coil is higher, still.  This same effect was extremely small with the stainless steel coil, further indicative of its lower Q_u.  

Comment:  It's worth mentioning that with higher "Q" coils, the physical aspects of the coil itself - namely the ratio of the length versus diameter, spacing between turns, material of the coil form, increasingly affect the Q - both for reasons of geometry (which can affect the amount of wire needed) and less obvious parameters such as distributed capacitance, etc.

Taking these Q_u measurements at face value, we can calculate the approximate "R" (resistive) loss of the two coils using the general formula:

• Q = X_L  / R

Or the more general form, knowing the inductance:

• Q =  2π f L / R
  

And rewriting this equation for R we get:

• R =  2π f L /Q

So, for a frequency of 6.6 MHz (which should be representative of 40 meters) and an inductance of 22uH, X_L is approximately 912 ohms, so for each of the two coils the apparent "R" value - which would be a combination of conductor loss and skin effect resistance we get:

• Original stainless steel coil:  R= 19.4 ohms
• Rewound coil (silver-plated wire):  R=4.1 ohms

The reader should be reminded that for ideal components, at resonance the reactance of the inductor is losslessly canceled out by the reactance of the capacitor so what we are left with - the value "R" mentioned above - will be the ohmic (conductor loss + skin effect) losses of the materials.  This also means that the "R" value will be added to the feedpoint resistance - and the effect of this "R" value is to lose power as heat as we will see below.  It is not lost on me that the loss values appear to be far higher than those obtained from Owen Duffy's calculator if one presumes skin effect to be the main source of loss - which we know is not going to be the case. 

The ohmic loss mentioned above is not going to be the only source of loss in a real antenna system:  In the case of a vertical, the "ground" losses (ohmic loss of radials, dirt, etc.) and with any antenna, the materials from which it is constructed (wire, telescoping rods which are themselves stainless steel, any balun being used, etc.) will come into play - and for an "electrically small" antenna such as either the JPC-7 or JPC-12 on 40 meters, will dominate and probably be the main points of loss besides the coil.

This goes to show how - in either case - doing anything to physically "embiggen" the size of the antenna - such as making the elements longer (adding drooping wires to the loaded dipole, adding a tophat to the vertical) will reduce the amount of inductance needed and increase the radiation resistance - both things that will contribute to improved efficiency. 

With the stainless coil, it gets worse the lower you go!

Out of curiosity I re-did the Q measurements using a 270pF silver mica capacitor - which lowered the resonant frequency to about 2.2 MHz - and got the following results using method #2: 

• Original stainless steel coil unloaded Q: 29
• Rewound coil (silver-plated wire) unloaded Q: 277

Given the lower frequency and lower skin-effect losses I fully expected the loaded Q to be slightly higher - which is true for the silver-plated coil - but initially I did not expect the Q to go down on the stainless steel coil so I re-did the measurement using method #1 and got about the same results (to within a few percent) - but in retrospect, I realized that this was to be expected.

As Q_L can be defined as being the ratio between inductive reactance ( X_L ) and skin effect and ohmic resistance (R), if "R" remains pretty high and X_L lowers with frequency, the "Q" will be lower:  Since the resistance of the stainless steel wire is so high to begin with, it figures significantly in the reduction of Q and thus the losses incurred.

In perusing the forums in the back-and-forth discussions about stainless steel versus silver-plated coils, people have observed a "hotter" coil at the lower frequencies.  At first glance, this makes sense since lower frequency = "more coil" = more lossy wire - but the fact that - at least at HF - the Q of the stainless coil goes down significantly with frequency makes it even worse!

Testing with the JPC-12 vertical and JPC-7 loaded dipole.

As noted earlier, the rewound coil was initially tested on the JPC-12 loaded vertical on 40 meters - mostly because it uses only a single coil and at that time I had rewound only one with silver-plated wire.  While I was at it I decided to see if I could detect any difference in the current flowing through the coil at a given RF power output related with the use of the original (and lossy) stainless steel coil and the silver plated coil.  Again, figure 7 shows this rewound coil with a thermal infrared camera just after a 60 second key-down at 75 watts, the temperature rise being just 3F (<2C).

Let us now consider the measured resistive losses of the coil (let's say 20 ohms for the stainless coil, 4 ohms for the silver-plated one) at 75 watts - the power at which we observed the temperature rise.  As we know the approximate current to be expected (about 600mA at 20 watts as measured with a known-accurate thermocouple-type RF ammeter) we can calculate the apparent losses at 100 watts which would equate to about 40 watts for the stainless coil and 5.7 watts for the silver-plated coil.  What this means is that nearly half of the power is lost in the stainless steel coil - but this still represents less than 1 "S" unit of loss. ^{Footnote 2}

Note:  Judging by the ratio of the temperature rise between the two coils (3 degrees F for the silver-plated coil and 110F for the stainless) we would expect far greater difference in power loss between the two coils (more than 30-fold difference, so I'm likely missing something here).

Once I had two silver-plated coils and two stainless steel coils, I could do a direct comparison on the JPC-7 loaded dipole. The JPC-7 is more or less a pair of JPC-12 vertical on their sides, fed with a balun - but rather than having the ground (radial) system to "push" against when radiating RF, it - being a dipole - used both elements against each other and the "ground" under - unlike the vertical where the ground/radial participates directly in current flow - is somewhat less affecting of the impedance, although the proximity of the ground does have the effect of lowering feedpoint resistance and resonant frequency.  (As we are concerned only with "feeding" the antenna, we will ignore the antenna pattern.)  

With the original stainless steel coils, the feedpoint resistance at resonance is "close enough" to 50 ohms to keep a radio without a tuner happy (it's actually lower than 50 ohms as noted below) - but consider that this means that each half of the dipole is closer to 25 ohms, the two being in series with each other:  With two coils' losses now in the mix - and the fact that a given loss of a coil in a 50 ohm circuit as a percentage was about half that of the same amount of resistance in a 25 ohm circuit - the losses are arguably worse, but "split" between the two elements.

While I didn't have the opportunity to use the thermal infrared camera to measure the temperature rise of the stainless coils on the JPC-7, they both got rather hot to the touch after key-down at 75 watts, indicating a roughly comparable amount of loss as did the original stainless steel coil on the JPC-12 vertical:  As with the vertical there was little change in temperature of the silver-plated coils.

Using a NanoVNA and minimal coax length  ^{Footnote 3} I set up the JPC-7 as per the the manufacturer's instructions on 40 meters:  From the feed point there were two mast sections, the coil and then the telescoping rod on each side.  Carefully setting the coils and the element lengths to yield the lowest "R" value (e.g. at resonance), I then noted the "feedpoint" resistance at resonance (where reactance, or "J" = 0) using the stainless steel and then the silver plated coils:

• Stainless steel coils:  38 Ohms (1.32:1 VSWR)
  
• Silver plated coils:  15 ohms (3.4:1 VSWR)

It's worth noting that these "feedpoint" readings were taken with the supplied 1:1 balun inline along with a short length of coaxial cable so the above readings are NOT precisely those of the actual feedpoint resistance:  There is likely a bit of loss and transformation occurring in the aforementioned set-up so the absolute numbers above may not reflect the actual feedpoint resistance itself.  I also observed that on the JPC-7, the (normalized) 2:1 VSWR bandwidth was lower with the silver-plated coil - an expected effect with higher Q resonator coils.

Note:  On higher bands (e.g. 20 meters and up) the feedpoint impedance was much closer to 50 ohms with either coil and it's likely that nothing special will need to be done to keep a radio "happy".

One might be tempted at first to think that because of the higher VSWR,the silver plated coil constituted an antenna that was "worse" - but that would be wrong - this actually indicates the opposite.  What this measurement shows us is that the apparent total resistance of the two silver plated coils at 40 meters was 23 ohms less (about 11.5 ohms for each coil) than that of the silver plated coil - and this increased resistance is what accounts for the power being lost as heat.

This realization still leaves us with the problem that if we take away much of the loss of the coils we lower the feedpoint resistance which means that we can end up with a rather high VSWR - of over 3:1 - meaning that many radios won't be particularly happy with the situation without throwing a tuner into the mix.  This leaves us with several options:

• Pretend we didn't see this and continue using the stainless steel coils.  This is an obvious choice and I can attest that both the JPC-7 and JPC-12 antennas do work pretty well despite the loss of the coil, but personally, I can't "un-see" the lossy nature of these coils, so that's not an option for me.  As a "portable" antenna is all about compromise of performance, I prefer to minimize the deleterious effects of as many aspects of this "compromise" as I reasonably can.
  

• Use an antenna tuner.  Placing a tuner at the antenna is the preferred choice as it will minimize mismatch losses that will result if the tuner is placed at the far end of the cable feeding the antenna (e.g. in the radio.) Whether the magnitude of mismatched loss of the cable when the tuner is placed at the distal (radio) end of the feedline to match the lower-loss silver-plated coil is worse than using no tuner at all with the stainless steel coil cannot be easily answered without knowing the properties of the coax used and how a specific tuner works under the impedance conditions that it might see.
  

• Rework the balun.  The JPC-7 has a 1:1 balun (one that isn't very "balanced" - but that's another topic) but it is clear that you could  choose a balun that inherently provides a suitable transformation - but more than one such balun would be required to cover all bands.
  

• Autotransformer.  A tapped autotransformer used to be a common "thing" many years ago for matching short verticals (e.g. mobile installations) to deal with the low feedpoint resistances at resonance - often well under 20 ohms for a low-loss coil.  These devices seem to be less common these days, but if you look carefully they may still be found on the surplus market - namely the Atlas MT-1 and Swan/Cubic MMBX, both of which offer selections of impedances that will easily yield 1.5:1 VSWR or better at any likely feedpoint resistance at and below 50 ohms.  I have tested the Atlas MT-1 (by putting two units back-to-back) and found a single unit to have about 0.2dB of loss on 40 meters which theoretically represents about 5% power loss.  (Useful articles about RF autotransformers may be found in the November 1976 issue of "Ham Radio" magazine - link and the December, 1982 QST - link.)

As mentioned previously, the losses of the stainless steel coil are "about an S-unit" on the lower bands so the user would have to weigh the benefits of the potential losses incurred by matching a silver-plated coil and additional matching versus just using the stainless steel coil and getting a more convenient match and just "eating" the losses.

We take a road trip to northern Wisconsin to discover the origins of the Wolf River and then follow the scenic waterway downwards in this entertaining Parks on the Air activation.

Build a Wolf River Sporty Forty bypass wire: https://youtu.be/m8Y_dDCBlvo

Feather Flag Base: https://amzn.to/3MdepHE
Wolf River Sporty Forty Coil: https://www.wolfrivercoils.com/
MFJ-1979 whip: https://amzn.to/3B9cehF
42×108 inch Faraday Fabric: https://amzn.to/3Vt1m9R
Jaw Mount Antenna Clamp: https://amzn.to/3VL5Ir6
SO-239 stud mount for jaw clamp: https://amzn.to/3VT1KwG
Contact logging: https://www.hamrs.app

As a bonus, patrons can view the unedited phone contacts for this POTA activation. Visit my page on Patreon for details: https://www.patreon.com/kb9vbrantennas

I do return QSL, if you made a contact with me and would like a QSL, please send me one. Return postage not necessary, but always appreciated. As they say, KB9VBR is ‘good in the book.

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The post Exploring the Wolf River: A Parks on the Air adventure along a scenic waterway appeared first on KB9VBR Antennas.

The JPC-12 antenna (possibly made by BD7JPC) is relatively inexpensive a portable vertical antenna - made in China, of course - that may be found for sale at quite a few places  under a few different brand names (including "Chelegance"). The price varies very widely - sometimes well over $200 - but I got mine via AliExpress for about $120, shipped, about a year and a half ago.

Note: 

I analyzed the JPC-7 loaded dipole antenna - which is made by the same company and uses many of the same components - and reported on it in previous article, and you may find that discussion HERE.

Silver-plated coils:  Since this article was posted I have added an article describing the effects of the stainless-steel coils and how to rewind with silver-plated copper, found HERE.

Figure 1: All of the standard components of the JPC-12 kit. Click on the image for a larger version.

As for a vertical antenna, there are only so many variations on a theme.  The JPC-12 is intended to be used as resonant vertical, and with its included coil, it is capable of operation down to 40 meters - but it can be operated sans loading coil at higher bands, adjusting the length of the telescoping section to resonance.

"The perfect is the enemy of the good"

The above statement should be kept in mind when doing any temporary, portable installation.  The idea is to have an antenna that will work "well enough" to do the job.  It's also likely that in the situation where you are portable, you will not (and cannot!) spend an inordinate amount of time tweaking things to eke out the last decibel.

This is not to say that one should not be mindful of good practices as too much corner-cutting can excessively impact performance and potentially replacing enjoyment with frustration.  One should achieve a balance between that which works well and something that will allow more operation than fussing about.

Remember:  The more time you spend trying to get that last bit of performance out of your system is less time that you are spending operating - and I'm presuming that operating is your goal.

What is included with the JPC-12

As shipped and as depicted in Figure 1, the antenna comes with these components:

• Aluminum ground stake.  This is a pointed stake 9-5/8" (24.5cm) long end-to-end about 1/2" (1.3cm) diameter.  This stake has M10-1.5 (coarse) threads on the end - the same as all other male and female threads used on the other mast/coil components of this antenna.
  

The use of elevated radials is arguably most important on the lower frequencies of operation of this antenna - namely 40 and 30 meters - where efficiency of this "electrically small" antenna will suffer due to a number of factors, but maximizing the efficiency of the ground plane is one way to mitigate this.  In those cases where it is not practical to elevate the radials, the wires may simply be laid atop the ground.  

As these posts are intended for marking driveways they are bright orange, making them stand out, but near the top they have a piece of white reflective tape so that they will show up at night.  As I had this type of tape on hand I added a piece to the bottom section as well - just below the stainless steel capillary tube - to make them even more visible - particularly if the bottom and top portions are used separately to mark where an on-the-ground radial might be run to warn against a possible trip hazard.

The use of a "Magic Carpet" (e.g. "Faraday Fabric")

There is no reason why one could not use the aforementioned conductive fabric as part of their ground plane - but you would probably have to construct an additional component to connect to the fabric and use it effectively.  For this, a piece of clean aluminum or copper plate laid atop the fabric - possibly weighed down with a rock - should provide a low-impedance connection to it.

While I do own some of this "Faraday Fabric" (obtained from Amazon) I have yet to try it with this antenna - and when I do, I plan to perform an "A/B" comparison.  As of the time of this writing I have yet to see a serious, scientific and well thought-out comparison between a simple radial field and the use of just the fabric:  Most of these comparisons simply demonstrate that it is possible to get a good antenna match while using the fabric - but as we all know, simply getting a match does not mean that the antenna will work:  After all, a dummy load has a great match!

I expect that - at least on the sort of desert ground that I'm likely to encounter - the radials will "win" the contest - although I still plan to do a comparison:  I suspect that using both the fabric and radials will offer decent results - even when tuned to a higher band for which the lengths of the radials are not expected to work (e.g. 20 or 10 meters with 40 meter radials.)

Additional antenna height - both real and "virtual"

Figure 8: The accessory top had kit consisting of a machined piece that attaches to the top of the vertical with four telescoping rods. Click on the image for a larger version.

Any antenna that has to be electrically lengthened with inductance is likely to suffer from efficiency loss as that inductor is unlikely to be comparatively lossy.  As the antenna is mechanically "about" 1/4 wavelength on bands above 20 meters, it make sense, then, that the lower bands that it is intended to cover - particularly 30 and 40 meters - need some additional inductance to bring it to resonance.  It further follows that anything that may be done to make the antenna "taller" will reduce the amount of needed inductance and minimize these losses.

Tophat capacitance

Another accessory available for this antenna is a small tophat attachment for the telescoping vertical section.  Often described as a "PAC-12 Capacity Cap" this consists of what looks like a knurled aluminum knob with five holes drilled around its circumference and yet another hole on the bottom sized to receive the "static ball" (really a short cylinder) atop the telescoping section.

Using a set screw to secure it to the top of the antenna, this kit contains four small telescoping whips (3-1/8" 8 cm long collapsed, 12-1/4" 31c fully extended - not including threads) that screw into the 5/8" (2cm) diameter center disk.  Assembled, the end-to-end length of two of the telescoping elements is 25" (98.4cm) which forms a four-spoke "disk" that adds to the effective height of the main telescoping section of the antenna by increasing the capacitance.  The idea (and hope) is that this allows the reduction of the amount of inductance needed to bring the system to resonance - and it also allows potential coverage of 60 meters as noted later.

The size and weight of this attachment is, in my opinion, about right:  Any larger or heavier, it would likely be too much for the fully-extended main whip to handle and expose it to excessive wind loading.  To be sure, one must always be very careful when handling the whip when fully-extended, anyway and adding the tophat increases the risk of damage.

Figure 9: The top hat kit assembled - but the rods are not extended. Click on the image for a larger version.

Testing has shown that the addition of the tophat - when the antenna has previously been tuned for 40 meters - lowers the resonant frequency by approximately 1 MHz indicating an increase of virtual height by about 12 percent at that frequency.  Even with the tophat the antenna falls short of being able to resonate at any 60 meter frequency with the normal complement of parts included with the antenna.

For the higher bands, the top-hat may be enough to eliminate the need for the coil on 20 meters - or at least greatly reduce the amount of coil and thus the potential loss.

Of course, the use of this top hat means that the existing coil marking scheme (e.g. the paint marks that show approximate slider position for the bands) is meaningless as tuning is changed - but if one is already prepared in the field for this (e.g. using an antenna analyzer, added markings to the coil for the new configuration, a paper template marked with pre-determined coil positions) then this is of little consequence.

This tophat kit is constructed fairly well, using a small grub screw with a supplied Allen key to attach it to the top of the telescoping section, but I noted that the key and the screw weren't well matched and couldn't be tightened too much with the key slipping.  Rummaging about in my collection of hardware I found several metric machine screws and a hexagonal brass stand-off with matching threads and I replaced the grub screw with the stand-off, allowing it to be attached firmly to the top of the telescoping section using just my fingers.

Additional mast sections

It should not be surprising to know that you can buy individual mast sections.  These are often described as being "dedicated lengthened vibrator for JPC-7 (PAC-12) multiband portable antenna".  I purchased two more of these sections when I first purchased the antenna, increasing its fully erect height from 13' 5" (411cm) to 15' 7-5/16" (476cm) and coupled with the tophat and the full inductance of the coil allows the antenna itself to resonate at approximately 4.7 MHz, allowing complete coverage of the 60 meter band.

Figure 10: Four more mast sections to be used in a variety of ways - as ground supports, or as the "live" mast itself. Click on the image for a larger version.

At this extended height and with the tophat, this antenna was used in fairly high winds with gusts of 35 MPH (approx 67 kph) with no issues:  Having clamped the ground stake of this antenna to a metal fence post helped keep the antenna vertical and minimize sway certainly helped!

After using the antenna several times, I purchased yet two more mast sections (for a total of eight) - not only to have as spares, but also to elevate the bottom of the antenna still further.  Living in the desert west of the U.S. (Utah) it's often the case that there is only sand into which the ground stake can be pushed and it simply isn't long enough to adequately support the antenna:  Lengthening the ground rod with the addition of another mast section allows the ground stake to be pushed in farther and support the antenna without burying the feedpoint below ground level or stealing one of the mast sections from the antenna and reducing its height.  This is mostly a problem on the lower bands (40 and 30 meters) where one needs as much height as one can get to maximize antenna efficiency.

This extension also facilitates the use of an elevated ground radial system, placing the feedpoint - and the ground radial disk - at a reasonable height.

Maintenance

The telescoping whip(s)

The telescoping whip is certainly the most fragile component included and it - like any other telescoping antenna - is easily broken if one is not careful.  The "safest" way to collapse one of these things is to pull it down - section by section - starting from the bottom:  One should NEVER push it down from the top as that is just asking for problems.

As with any telescoping whips that I own, one of the first things that I do when I get it is to make sure that it is clean of dirt and oxidation (particularly if it has been "pre-owned") as this can cause the metal-on-metal - especially when the two metals are the same - to gall and seize up, making it more difficult to extend or collapse.  If I do find a section that is hard to move, I carefully examine it, often discovering slight scratches, buffing them out with very fine sand paper (1000 grit or finer) and/or steel wool (size 0000 or finer).

The final step - after cleaning with paint thinner or alcohol to remove any dust - particularly if it was just buffed with steel wool or sandpaper - is to put a light coating of oil on all sections when they are fully extended:  I prefer to use a PTFE ("Teflon") based lubricant like "Super Lube" (made by Synco) as it does not dry and become "gummy".  Extending and then retracting the whip a few times does a decent job of spreading out the lubrication - even getting inside the individual sections.

Although much smaller, I did a similar thing to the four telescoping whips that comprise the tophat.

I would consider this "cleaning and lubricating" to be a necessary maintenance item when using this antenna, needing to be done occasionally, with constant vigilance toward possible issues every time it is used.

Inductor slider

The adjustable inductor's components are all stainless steel - including the coil wire itself.  Besides being known for the fact that this material "stains less" than others, it is also known for galling - that is, developing tiny burrs on the surface and jamming up when it is used against the same type of metal:  In the case of stainless screws, nuts and bolts - if these gall, even if you ARE able to remove them without breaking them, they have to be replaced.

While the contact area on the slider is small enough that it is unlikely to gall and get "stuck", I noticed immediately a bit of "roughness" in its movement that indicated excessive metal-on-metal friction:  I could not tell if this was on the contact area of where the slider rubbed across the coil's windings or on the sliding rod itself - but it was probably a combination of both.

This "roughness" in movement was relieved with the application of lubricant - the same "Super Lube" used on the telescoping sections - also making the adjustment easier to do.

Improving the coil

As noted previously, the coil is wound with 18 AWG (1mm dia) stainless steel wire.  It is suspected that one of the main reasons why this type of wire is used despite its terrible losses - as compared with copper - is that this resistive loss increases the feedpoint resistance - but at least in relatively cool temperatures (below 90F or 32C) I wouldn't worry about running key-down for several minutes at 100 watts - or higher power with a low duty-cycle mode like CW or FT-4.

As it happens, one can juggle the proportions of a vertical antenna a bit to vary the feedpoint resistance - but if you consider that these same coils are also used in the JPC-7 dipole, the reasoning behind the use of stainless steel wire becomes more clear.  An electrically-short dipole - such as when the JPC-7 is configured for 40 meters - would ideally have a feedpoint resistance of just a few ohms - but this would not match at all well to a 50 ohm system:  Even a very low-loss antenna tuner would have difficulty coping and placing the tuner away from the antenna through a length of coaxial cable would make the situation even worse!

Having said that, testing was done that revealed that on the JPC-17 - while operating on the lower bands (30, 40 meters) a significant amount of power was being dissipated in the coil - enough to raise its temperature by 135F (75C) at 70-100 watts on 40 meters (lower loss on higher bands) - but rewinding the coil with silver-plated copper wire pretty much eliminated that element of loss.

A future article on this blog will detail the rewinding of this coil along with measurements/comparisons between the original stainless steel and rewound coil for both the JPC-7 dipole and this JPC-12 vertical which will eliminate any nagging worries about power handling capability.

Using the JPC-12 vertical in the field

I have used this vertical in the field a number of times, mostly with the "augmented" kit with the extra mast sections, top hat and ground radial plate and elevated radials - typically on 40 and 60 meters SSB, but also for POTA using CW.  While the signal reports comparing my signal with that of others using full-size antennas unsurprisingly indicates that this doesn't to as well as the others on the lower bands, conditions have generally been good enough that there was little difficulty in copying my signal.

Figure 11: The JPC-12 vertical out in the wild in a slight breeze. The tophat is installed as is a section below the radial plate - along with extra sections to increase height. Click on the image for a larger version.

As the ground here in Utah is usually rather poor making it difficult to simulate the "other half" of a vertical antenna, it is even more important that the radial system be effective.  While I usually configure it to have four radials elevated about 18" (0.5 meters) above the ground, I have also simply laid the radial directly on the sandy soil - or found some convenient sagebrush, scrub oak or some other low plant or small tree to support them off them ground - and have always had pretty good results.

While I like this antenna, I find it to be far less convenient than the JPC-7 loaded dipole in that the vertical takes quite a bit more time to set up, needing a bit of assembly of the various pieces and laying out of the radials.  With resonant radials, changing bands - and trying to maintain optimal performance - also makes it a bit awkward by the fact that the radials need to be shortened/lengthened as appropriate/

Practically speaking, having the radials laid out for 40 meters and running on 60, 30 or 15 meters isn't much of a problem, but picking a band that is an even multiple of the radials' base resonant frequency - being an odd half-wave multiple (e.g. 20 or 10 meters with a 40 meter radial) - will not work well as that is the worst possible radial length (other than zero length) to choose:  The half-wave length will not provide the low impedance at the antenna and it's also likely that the coaxial cable will become most of the radial, possibly causing a "hot rig" in terms of RF and the related ill effects (RF into the audio, computer/radio crashing, extra noise) from doing so.

If, however, I have a bit of extra time and I want a better signal that I would otherwise get from the loaded dipole or a mobile-mounted HF antenna, I would definitely set up the JPC-12.

* * * * *

Related articles: 

•  I analyzed the JPC-7 loaded dipole antenna - which is made by the same company and uses many of the same components - and reported on it in previous article, and you may find that discussion HERE.
• Silver-plated coils:  Since this article was posted I have added an article describing the effects of the stainless-steel coils and how to rewind with silver-plated copper, found HERE.

This page stolen from ka7oei.com

[END]

I made over 1000 contacts and spent a month working with the Chameleon PRV or Portable Resonant Vertical Antenna kit. The core of the PRV is the Multi Configuration Coil or MCC. This adjustable coil, when paired with an appropriate length whip, will operate on any frequency between 6 and 80 meters. The PRV kit is well suited for outdoor and portable operations such as SOTA, Summits on the Air or POTA, Parks on the Air.

Chameleon PRV (Portable Resonant Vertical Kit):
https://chameleonantenna.com/shop-here/ols/products/cha-mcc

A Chameleon PRV POTA Kit was provided in exchange for this video.

PRV kit breakdown

The core component of the PRV or portable resonant vertical kit is the Multi Configuration Coil. The PRV is a base loaded antenna and the multi configuration coil, when paired with an appropriate sized whip, allows you to achieve a resonant match for any frequency between 6 and 80 meters.

The coil is constructed out of anodized aluminum outer body with a delrin center and stainless steel and silver clad copper wire. At first glance you will say this is Chameleon’s knockoff of the Wolf River coil, but i believe it is more appropriate to compare the PRV kit and multi configuration coil with the Super Antenna MP1. The MCC is a more refined and elevated version of the MP1 coil, with the addition of being manufactured in the USA.

The coil itself is fairly lightweight, weighing in at just under 16 ounces and fully collapsed, it is 12 ½ inches long. At the base of the coil is a 3/8×24 male thread for attaching it to a base. Their is an SO-239 or UHF female connection for the coax, a thumb screw to lock the outer body of the coil to the center. This will keep it from slipping after you have a match. And finally, a 3/8×24 female receptacle for a whip. The choice of whip you use will determine the frequency range of the coil.

Chameleon sells the PRV kit in three different packages, the MCC coil by itself, the SOTA, or summits on the air light kit, and the POTA, parks on the air heavy kit.

Assembling the kit

Assembling your PRV or portable resonant vertical antenna is pretty straight forward. If you have any experience with other base loaded verticals this will seem familiar.

First off is the base or antenna support. The PRV kit comes with a ground spike you can push into the ground to support the antenna. If you are working with soft earth, this stainless steel spike will the coil and up to the 17 foot whip. But, if you are like me, and it’s winter, or if you are operating on hard earth, or a durable surface like asphalt or concrete, the spike won’t work. The POTA heavy kit solves that with the UCM or universal clamp mount can be attached to anything with a lip, like a picnic table or bbq grill. The coil and whip can be deployed from that.

For my testing I preferred to use their new carbon fiber tripod. This is a lightweight portable tripod with extendable and adjustable legs. You can splay the legs out and it will easily support the coil and the PRV standard whip in most weather conditions. It will also support the 17 foot whip as long as it is not windy. If there is anything brisker than a gentle breeze, you run the risk of the tripod tipping over. Sand bags or weights on the legs will help prevent that. The tripod has a 3×8 x 16 course thread and ¼ inch male thread. These are standard tripod threads and the PRV kit comes with a ¼ inch to ⅜ inch fine thread adapter. You will use this adapter with the Chameleon tripod or any other tripod you wish to use.

Tuning

Tuning, or finding a good match, on your PRV can be easy, or it can be a challenge, it all depends on how you approach the process. I’ve had situations where the SWR in my vertical antenna drops down to nothing, and other times when it was a total bear and I can’t get lower than 2:1. I’m going to tell you right now, it’s not you, and often it is the location or ground conditions the antenna is on. That means if you are going to run with base loaded vertical antennas, you just need to accept that sometimes you won’t get perfect SWR, and in reality, anything less than 2:1 really is ok. Fortunately, Chameleon, with the PRV offers a fair amount of guidance in their user guide on how to get a good match on the various bands.

My experiences

So what is my experience with the Chameleon PRV or portable resonant vertical antenna? I’m going to say that I am very impressed. Honestly, this isn’t a one off review of the antenna, but instead my opinions after using for a full month and making over 1000 contacts with it. There are some things that I like, and some that I don’t.

First off, construction is top notch. This antenna is made in the USA and it shows with quality components. The multi configuration coil is well built, it is designed to handle up to 500 watts single sideband and 200 watts digital modes. I find that the construction of the coil and whip would support those claims. The documentation is excellent, it goes into great detail on how to tune and adjust the antenna, which is outstanding. The system is extensible, you can use it with the 58 inch whip, but I believe it really shines when you combine it with either the 9 foot Mil-Whip or 17 foot stainless collapsible whip. The 34 foot wire winder radial is innovative, but I think its also the weakest part of the package.

The problem I have with the wire winder radial is the weight. When you suspend it on a line from the elevated tripod to another support, you will need either a substantial tripod or to guy everything down as the weight of the winder on the line will pull the whole thing down. Since the ground was frozen during my test period, I couldn’t guy things, so I struggled with deploying the elevated radial system.

But the elevated radial system also seemed to offer the best performance overall, so the effort to put it up is worth it. Properly deployed, I found it easy to get a match with the elevated radial as you weren’t subject to the vagaries of ground conditions.

But I really like that the kit is extensible. You can add additional radials for better ground performance. I found that to really be a benefit for the 20 and 40 meter bands. You can use it with the magic carpet. I had a difficult time getting a good match with the faraday cloth and the 58 inch whip, but the ground screen worked great with the longer whips. And speaking of longer whips, I think the PRV is at its best when you use it with the 17 foot stainless or 9 foot mil-whips. I had no problems putting out great signals QRP, with only 5 watts of power using the long whips.

Bonus content and activation videos using the Chameleon MCC coil and the PRV kit are available to my patrons. Please visit my page on Patreon for details: https://www.patreon.com/kb9vbrantennas

Timestamp
00:00:00 Chameleon PRV Portable Resonant Vertical Antenna kit
00:00:57 CHA MCC Multi Configuration Coil
00:02:38 PRV SOTA Light and POTA Heavy Kits
00:03:36 Deploying the PRV POTA Heavy Kit with Extensions
00:05:52 Ground Spike, UCM, Carbon Fiber Tripod
00:07:55 PRV SOTA Light Kit Deployment
00:09:15 Tuning the MCC Multi Configuration Coil
00:11:01 Elevated deployment with the wire winder radial
00:12:35 My experience with the Chameleon CHA PRV POTA Kit

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The post Everything you wanted to know about Chameleon’s PRV Vertical Antenna Kit appeared first on KB9VBR Antennas.

(February 14, 2024) In the social forums, I often see the question posed by a newer POTA enthusiast asking if anyone does any Parks on the Air activations on the 80 meter band. This is a great question, as 80 meters is excellent for getting those local and regional contacts and it often is a band that is needed if you are interested in your N1CC award. But there are certain challenges with that band and they are multiplied when you go portable.

Being at the top of the solar cycle, 80 meters is relegated to being a night time band. During the day the noise floor is just too high for the weaker signal of an activator to compete. This is often compounded by the highly compromised antennas we end up using on the lower bands. There’s a reason why 80 meter aficionados use amplifiers: it’s to overcome the limitations of band noise and antenna losses. To top all that off, many parks close in the evening hours, making it even more challenging to activate a park on that band.

With all the challenges of 80 meters, I found myself in a spot where I had the time and ability to do a late shift at a local park, Rib Mountain State Park (POTA K-1473).

Late shift for Parks on the Air purposes is defined when Zulu day (00:00) rolls over. Here in the midwest in the central time zone, we are 6 hours behind GMT, Zulu, or Universal Coordinated Time, so at 6:00 pm local time (7pm when daylight saving time begins) is the start of the new POTA day. This late evening activation period is affectionately called the Late Shift, as it happens during the evening hours and the contacts count towards the next local time day.

On February 14, Christine was flying back from a business conference and her plane was expected to arrive at 9:00pm. I could have stayed at home and snoozed on the couch before picking her up at the airport, or I could make myself useful and activate a park. Fortunately my favorite local park, Rib Mountain State Park, is only 15 minutes from the airport, so I could be out until 8:30 or so, get on the air, and make some late shift contact. I grabbed a quick dinner and traveled up the hill for a couple hours of late shift.

Setup

Being it was the evening, my plan was 40 and 80 meters, two bands I don’t operate much from the mountain and two that will have good performance after sunset. Being this is winter and the ski hill is operating, I knew that I would have some noise on the 40 meter band from the chair lifts. Checking the schedule, the hill was operating until 9:00pm. My only hope was that they wouldn’t be operating the lift on the far west side of the hill. If it was, my only recourse would be to operate digital on the 40 meter band as the chair lift noise all but blanks everything out.

Sure enough, when I got to the top of the hill, there was plenty of activity near the park entrance and the two large high speed lifts were running, but driving to the other end of the park, everything was dark. The parking area was unlit and the 3rd high speed lift was not in operation. Excellent! That meant 40 meter phone operation was on.

For My setup, I used the 213 inch whip paired with the Wolf River Coils Silver Bullet 1000 coil. I needed the extra length of the SB1000 for 80 meters, so that was the perfect choice. The longer whip meant that the coil would be somewhat efficient as I wouldn’t have to drop the collar all the way to the bottom to get a match. Sure enough, on 40 meters, I only needed about an inch or so of coil and on 80m, the collar was at about the 3/8 point, of just under half way down. I had both my window screen ground network and length of Faraday cloth (magic carpet), so I laid both down under the antenna to increase the surface area of my ground network. This was an excellent choice as the SWR on both 40 and 80 meters was under 1.5:1.

For transceiver, I put the FT-891 on the dash of the car, set the power of 50 watts, and started calling CQ on the 40 meter band.

The Activation

I was on the air 00:49 (6:49pm) and made my first contact 2 minutes later. To say that hunters weren’t looking for late shift activators is an understatement. For the next hour I averaged about 2 contacts a minute and racked up 95 contacts for the almost one hour period that I was on the air. Propagation was quite good and I easily worked stations on 40 meters that I often hear on 20 meters during the day, including a few west coast stations: California, Oregon, and Arizona.

Since the purpose of me being on the hill at night was 80 meters, and since I also had a hard deadline to keep, at 7:45pm I changed bands. At this time it has started snowing on the hill. We were expecting some rain/snow mix but the forecast said it would start after 9:00pm. Evidently it got here a little early as my ground screen and cloth was covered by a light dusting of snow. Moving the collar down to 80 meters, I got a good match, and the snow didn’t seem to affect anything. I was ready to rock and roll.

Band conditions on 80 meters was excellent that evening. My noise floor was about S2, which is amazing, and many of the hunters I got on 40 meters followed me down to 80 for another contact on that band. I operated for 40 minutes and got 26 in the log. A little slower pace than 40 meters, but expected with the shorter coverage the 80 meter band offered. By this time is was 8:30pm and my wife was expected to land in 30 minutes.

But as I mentioned, it was snowing, and that same snow delayed her flight out of Minneapolis. I now had about an extra half hour before I needed to be at the airport. There was only one reasonable thing to do, work another band. I needed 30 meters at the park for my N1CC, so I retuned the coil, hooked up the Digirig, and got 8 30 meter FT8 contacts in the log. Signals were really good on 30 m that evening and the passband was full of activity. I secured at 8:54pm. According to Flight Aware, she would arrive at 9:20, so I had just enough time to pack up, head down the hill, and get to the airport.

Conclusion

Late shift on Rib Mountain was a lot of fun. Getting down off the hill in the snow was not. By this time it was snowing pretty good, but taking things easy and the confidence of the Outback’s all wheel drive made the day. I arrived at the airport at 9:24pm and only had to wait a minimal amount of time while Chris got her luggage.

There is no camping on Rib Mountain, but the park is open until 11:00pm. Until this point I never really thought much about going up there for a late shift activation, but with the results of this one, I certainly am going to do it again. The vertical with the SB1000 coil was an excellent choice and I feel adding the second screen to the ground network made a big difference for the low bands. I will certainly do that trick again when I use the vertical on 80 and even 40 meters.

I got 129 contacts that day: 95 on 40 meters, 26 on 80 meters, and 8 on 30 meters FT8.

K-1473 Rib Mountain State Park 40 meter Late Shift Phone contacts

K-1473 Rib Mountain State Park 80 meter Late Shift Phone contacts

Map visualization of contacts courtesy of qsomap.com

If you go

Rib Mountain State Park
149801 State Park Rd
Wausau, WI 54401
State Park Pass required
Park open 6:00am to 11:00pm

The post Late Shift on Rib Mountain appeared first on KB9VBR Antennas.

We examine the differences between the original and higher power version of Wolf River Coils' Silver Bullet 1000 tunable loading coils.

The post Wolf River Coils – Silver Bullet vs. Silver Bullet Platinum 1000 appeared first on Ham Radio . Magnum Experimentum.