Having dipped my toes in to 10GHz EME with an existing antenna rotator I used for VHF/UHF LEO satellites I was faced with the need to upgrade my setup if I wanted to do it more reliably.

It was possible to make contacts with my existing setup, but the instability of it on a thin aluminium pole that moved like a pendulum in wind along with an inaccurate (for microwave use) rotator with a high amount of backlash and tracking errors were were a real annoyance. The rotator wasn’t meant for this sort of use so I am still happy it seen me off to a good start on 10GHz EME without a significant initial expense that may have put me off even trying.

There did not appear to be many commercial amateur radio rotator options at 0.1 degree accuracy with low backlash that I would want for my current, or larger dish, and those that might be suitable came with an eye watering price tag. So I made the decision to try to DIY it, mostly copied from people smarter than me with very few original thoughts.

I later noticed all a commercial option using slew drives from RF Hamdesign but I had the drive and parts here by that point so couldn’t take the easy buy my way out of the problem option.

Dual Axis Slew Drive

Having seen discussion on the moon-net reflector about options, I settled on using a dual axis slew drive rotator which seems to be a very popular choice at the moment. These seem to be mainly provided for use rotating solar arrays so they are fairly common devices, are not expensive and do the trick for radio use very well. It will also be suitable should I upgrade to a larger dish in the future.

The rotator was ordered from CoreSun drive and I settled on the SVH3-62B-RC-24H3033-REV.A as described at: http://www.coresundrive.com/en/product/Solar_Tracking/2019/0729/93.html

In its standard form this is slow for general amateur radio use, requiring a full 21 minutes for a 360 degree rotation, not handy for contests or LEO satellites requiring quick repositioning. They can however be ordered with different gearing to allow faster movement but as I’m using this for the slow moving moon I stuck with the standard option.

After payment was made, air freight took about a week to deliver the small but heavy crate at which point it sat a month or so as I looked at other peoples installations and figured out how I make use of it.

Dual Axis Slew Drive Documentation Errors

One thing that was a bit confusing was the wiring colours on the document supplied with the SVH3 did not match the wiring colours on the SVH3 I received. After some testing found them to be as follows:

Wire Definition

Pin 1 (black) = motor –
Pin 2 (red) = motor + 24V
Pin 3 (grey) = hall GND (marked yellow on document)
Pin 4 (brown) = hall + (5-12V)
Pin 5 (blue) = hall A
Pin 6 (orange) = hall B (marked green on document)
Pin E (green) = GND (marked grey on document)

Additionally, the gear ratios on the document supplied did not match that marked on the drives that arrived! I didn’t pick up on this until everything was mounted and in use so my calculations for pulse counting were initially off causing my some added bother.

Physical Mounting – Dish

I don’t have metal working skills or tooling beyond a wonky bench drill press so chose to create the antenna mount out of aluminium plate and angle that I could easily drill. One of the successful setups I had seen online and liked the look of was that of N5TM and chose to implement a similar mount for the dish with two plates bolted on to the size of the rotator. He describes the mounting setup and provides drawings of what he’s used top and bottom on his website here: http://n5tm.com/index.php/2023/10/30/brackets/

By printing the template to scale and centre punching I was able to mark the positioning of the 6x11mm holes of the rotator on the aluminium arm to check and drill. This wasn’t quick on my drill press but I managed it with only one hole being slightly off requiring enlarging. I chose not to trim the corners of the mounting arms off at this stage as they might be useful for fitting some physical stops later.

The Andrews 120cm dish has four mounting holes in a 14cm rectangle so I chose to use a solid aluminium plate affixed to the two arms with some aluminium angle.

The end result with the coach bolts that will attach it to the dish.

One mistake I made was with the length of the support arms, I reduced them in size a little from the diagrams I was working from purely due to delivery costs on the aluminium jumping up significantly thinking a small change wouldn’t matter with a small dish. Well it does. As a result I can only go down to 5 degrees elevation before making contact with the mounting pole. As I don’t have terrestrial microware possibilities here, and my moon horizon is minimum 8 degrees at 10GHz, it’s not a problem for now.

Rotator Controller – K3NG

I’d seen some commercial controllers mentioned along with some peoples very nice looking DIY setups and settled on the open source K3NG rotator option. This offers a lot of options for customisation, and is well documented.

I decided to use a Nextion touch screen display like I’ve used in other projects using VK4GHZ’s awesome code for the rotator available at https://vk4ghz.com/vk4ghz-nextion-for-k3ng-rotator-controller/ and not have any buttons to simplify things a little. The schematic from N5TM available at github helped me get my head around what was needed quickly.

I initially acquired a very cheap second hand 24v Meanwell PSU to use for the rotator, which turned out to be terrible RF interference wise on HF. Buy cheap buy twice.

I also used an RTC on the Arduino in order to allow the K3NG software to track the moon without needing a computer doing the tracking. This all came together in a big mess on the desk but both axis rotated as expected.

One thing I found was that the K3NG would not work with the INCREMENTAL_ENCODER option as I assumed it might as it requires a Z from the encoders. Patching the requirement out like someone else did made it kind of work but introduced some really odd problems I couldn’t get to the bottom of.

Using PULSE_INPUT with one line seemed to work okay and others have had success with this. Unfortunately it turned out I wasn’t to be one of them.

I designed a case with a sliding lid to house the Arduino, Nextion display, optoisolator, relay board, buck converter and connections and 3D printed it. In the unlikely event someone wants this, the STL is available here.

The Arduino would blip the relays on power up and I couldn’t figure out a way to stop this. I couldn’t detect the rotator moving during the short blips but decided not to chance it and settled on a small relay board with a timer to delay powering the relay board up until after the Arduino had booted.

Here is the mess complete for testing before sorting the cabling out.

Cabling

I picked a small waterproof enclosure with mounting wings that allowed it to be cable tied to the motors and affixed a terminal block inside this along with 4 holes and waterproof cable glands. I will attach it to the support pole when fully set up.

I had decided to use two separate cables for the controller, one carrying the pulse signals, the other power to reduce the risk of pulse signals being messed up, not sure if this actually helped or not. I understand many upgrade the rotator to have absolute encoders for accurate position feedback, or add external elevation detection but I’m going to run with it as is now and I don’t foresee it being too much of a problem with a 1.2m dish. (I was wrong)

Physical Mounting – Base

My setup is a little unusual in that it sits above a flat roof of a garage in order to get over the top of nearby vegetation and my house. Being on a flat roof accessed by a window in the house allows easy access to the setup. In order to have a vertical pole mounted on TK brackets with the pole going to the ground to support the weight, it needs to be 3.8m long with 1.8m of this above the top bracket. The aluminium pole I had been using was not sturdy enough to support the rotator and dish above and had an alarming amount of movement in even moderate winds.

I settled on 10cm steel box section to give me something that wouldn’t move. On asking g4ytl about how he mounted his dish I seen he had used similar box section with metal plates on top, one welded to the box section, the other plate bolted in to the rotator with both connected using bolts. There were a number of variations of this setup online and I liked the simplicity of it so went this route.

The box section will sits on top of an existing 40-50cm deep concrete slab that I can’t dig up to fit any sort of base support.

After deliberating for a few weeks about whether I should take up welding to make something up myself I decided I’d rather my first welds didn’t have a lot of expensive equipment/or me relying on them to hold and instead asked a local metal fabrication shop to do it. I was pleasantly surprised as it ended up costing not much more than the metal would have cost me and on speaking to them about the difficulties in welding thick steel I’m glad I didn’t try. I did however make a mistake with the wall size at 6mm with 10mm plate as it made the section ridiculously heavy requiring me setting up a winch on the side of the house along with some creative guide cables to raise it in to place.

I decided to use existing TK brackets that required drilling out new holes in the arms for the large U bolts to hold the section. As it’s on the inside corner of a wall I’ve also added extra brackets to the adjoining wall to have it fixed in place from two sides using a mix of resin fixings and wall bolts.

The Final Setup

And here it is ready to start testing. Some physical stops will be added once I’m happy everything is okay.

Follow-up

After using the setup for a month including making a number of EME QSOs without many of the difficulties that plagued my previous setup and being far happier with the stability of the setup, I was still having some problems.

The pulse counting seemed to be very quickly losing my position after lots of moon tracking movements as if there was over/under counting going on, especially in elevation. I also had an of instance of an unexpected jump in position that never repeated. To potentially fix the potential pulse counting issue I considered a master/slave setup to reduce the cable length the pulses had to travel.

For the elevation side I also considered getting and using a HH12-Inc for an absolute readout and giving up on the pulses there but failed to acquire one. Additionally one of the relays gave out bringing forward my plan to use H bridges instead of relays. While these problems were in my mind and I was waiting on the H bridge bits arriving I discovered the Arduino itself was causing RFI (I’d assumed it was the PSU) around the IF the 3cm moon beacon I use for testing.

At this point wanting to just get reliably operational quickly I decided to shelve the controller, which I really do like, and I know works for others on 3cm EME so could be made to work better with some more time. I plan to use it with my VHF/UHF satellite setup in the future or for anything else requiring a versatile easily configured controller system.

The new controller system, WinTrak with two MABMPU boards and the controller software running on a touchscreen Pi, has been working well for a few weeks with no obvious issues or requiring adjustments during a moon pass. This solution was pretty much plug and play so I don’t have much to say other than it works!

References

N5TM

K3NG

VK4GHZ

A rotator is a handy device used in ham radio communication systems to change the orientation of an antenna. Rotators have two parts, the rotator unit and the controller. The controller is normally placed near the radio equipment, while the rotator is mounted on the antenna mast below the antenna. It’s a must-have for DXers and operators who want to extend their reach and improve reception.

Is it Rotator or Rotor?

Let’s settle this before we move on. Hams tend to use both words interchangeably, but there is a subtle difference.

• A rotator is a device, such as a motor, that makes something rotate—like a mast with a Yagi attached.
• A rotor is a part of a device that rotates, such as a brake rotor or armature.

How Does an Antenna Rotator Work?

The rotator is typically mounted on the antenna mast or inside the tower, directly below the antenna, while the controller is usually placed in the ham shack near the operator’s position. The controller sends signals to the rotator unit, instructing it to rotate to a chosen heading.

Modern rotators are generally small. Due to gear reduction, the motor mechanism can be relatively compact and not draw much current. Large rotators have bigger motors, but the increase in strength is mostly due to improved gear and brake systems. The power required to turn even those big, stacked arrays is not that much.

To keep rotators from twisting in the wind, they include a braking mechanism. Smaller ones use a friction disc arrangement—when the rotator turns, the discs move apart to let the mast turn freely. When power is removed, the discs clamp together again. With medium-sized rotators, brakes consist of a heavy-duty solenoid with a spring-loaded wedge or bar that fits into indentations inside the rotating housing. On big rotators, worm gears are used and braking is done by the resistance to the gears turning backward under load.

Rotators are designed to turn a full 360 degrees, and often a bit more. That is known as overlap. At the ends of rotation, mechanical limit switches open to remove power from the motor. It’s important to leave a rotator loop in your feedline during installation to prevent stretching or breaking your feedline.

Choosing the Best Antenna Rotator

Durability is important, especially for something that’s exposed to the elements. Look for sturdy materials which can endure outdoor conditions without corroding or deteriorating over time. Opt for models with a sealed housing to protect internal components from moisture and dust for long-term reliability and performance.

Make sure the rotator you choose is compatible with your specific setup. This includes assessing antenna size, weight, and mounting considerations. There’s nothing more annoying than finding that your rotator won’t fit properly inside your tower. Also verify compatibility with any existing hardware you plan to use, such as controllers, accessories, and mountings.

It’s important not to overload a rotator. If you live in a location that’s subject to high winds, continuous winds, or large gusts, look at the wind load recommendations included with the unit. These are usually specified as a maximum antenna area in square feet or square meters. Add all of their wind load numbers together for several antennas on a single mast, and don’t forget the mast’s wind load. You can find your antenna’s specs in the manual or online.

A rotator can handle a larger wind load when mounted inside a tower section, as opposed to mast mounting, since the tower holds the mast in place straight above the rotator. Using a thrust bearing keeps most of the load off the mast, further increasing wind load capabilities. Inside tower mounting eliminates any sideways load on the rotating assembly relative to the base.

In the preferred tower-mounting configuration, a sleeve bearing provides additional support. Another option is using a thrust bearing at the top, which transfers the weight of the antenna and mast onto the tower and off the rotator. The rotator then just turns the antenna without the extra load.

Controlling the Rotator

Each manufacturer of rotator/controller combinations has its own design of control boxes for controlling the rotator and displaying antenna position. Yaesu’s desktop controllers provide a round dial with a 360-degree radial indication of antenna azimuth bearing. Hy-Gain HAM-IV and CD-45II models include a more traditional analog meter readout with N/S/E/W markings and azimuth readings in five degree increments.

There are also aftermarket control units that operate with many different rotators. These include the Green Heron RT-21 Series Digital Controllers and the EA4TX ARS-USB Rotator Controller with digital readout. The coolest of the group is the microHAM ARCO Advanced Rotator Controller (below) with touchscreen LCD control and azimuth information superimposed on a world map display.

If you’re old school, you may want to control your rotator manually with the clockwise/counterclockwise buttons or do point-and-shoot using the preset dial. If you plug in the call sign of a station, most logging programs will provide you with the short path and long path settings you’ll need.

Newer rotator controllers may have an interface—either RS-232 or USB. Some controllers can be connected directly to your PC to operate your unit. Older controllers may require an additional interface board that can be installed inside the rotator control box. For example, programs like PstRotator and DX-Lab can directly calculate the beam direction for long and short path and pass it on to the rotator control. Many of the popular logging software programs can also control a rotator with the help of a PC. The Ham Radio Deluxe Software suite for Windows includes the HRD Rotator Control module, which manages beam headings via any computer-interfaced rotator controller.

Interested in space? An antenna rotator with both rotational and elevation controls, like the Yaesu G-5500DC (plus related software), is essential for ham radio satellite, ISS, and EME (moonbounce) communication. It enables users to accurately track satellites and the ISS as they move across the sky. Such equipment can make adjustments quickly, maintaining a solid connection for communication.

What’s Right for You?

Decide what antenna(s) you plan to put on your mast or tower and calculate the total wind load. It doesn’t hurt to go a bit larger on your rotator. You’ll have some additional headroom and prepare for the possibility of an antenna upgrade or added antenna later on. It’s difficult to change out rotators on a tower—I know from experience.

Rotator packages usually include the necessary connectors. You’ll need to supply the wiring between the controller and the rotator, usually a six- or eight-conductor for ham rotators and three- or four-conductor for TV/light-duty rotators. They can be purchased by the foot or as ready-made cables. Other items to consider include thrust bearings and rotator shelves inside tower mounts, like the DX Engineering Accessory Shelf below for Yaesu and Hy-Gain rotators.

Light-Duty Rotators

For smaller VHF/UHF Yagis and rotatable dipoles with wind loads >3 sq. ft. Mast/inside tower mount.

• Hy-Gain AR-40, AR-500

Medium-Duty Rotators

For Hexbeam, tri-band 3-element monoband Yagis, and larger VHF/UHF arrays with wind loads of 8-10 sq. ft. Inside tower mount.

• Yaesu G-450ADC
• Hy-Gain CD-45II

Medium/Heavy-Duty Rotators

For multi-element Yagis with wind loads of 15-22 sq. ft. Inside tower mount.

• Yaesu G-800DXA
• Hy-Gain HAM-IV

Heavy-Duty Rotators

For large Yagis, multiple Yagis with wind loads to 35+ sq. ft. Inside tower mount.

• DX Engineering RT4500HD
• Yaesu G-2800DXA

Editor’s note: The DX Engineering RT4500HD rotator comes in combos which include rotator and 2-inch or 3-inch mast clamp; rotator, clamp, and ARCO controller (below); and rotator, clamp, and DX Engineering controller.

The post Doing a Good Turn: Choosing the Right Rotator for Your Amateur Radio Station appeared first on OnAllBands.