During one of our many lockdowns (because of COVID), I decided that I wanted to put up a semi-decent Satellite Ground station at my QTH. I’ve been playing with satellites for a while mostly using a handheld Yagi running around in the backyard all hours of the day and night. It was a bit of a cumbersome setup though, especially when the weather was bad. It was time to put something new together based on the following requirements:
- Az/El Control of a 2m and 70cm Cross Yagi
- Automated tracking of Satellites
- Capable of making FM and SSB contacts
- Satellite Telemetry
- Affordable (within reason, this is an expensive hobby)
The first part of the new satellite station was to figure out what to use for the rotator. You get some really nice Azimuth/Elevation rotators like the Yaesu G-5500 rotator. But upon closer investigation it seemed those are tricky to find in South Africa, and importing them gets expensive really quickly. I decided to rather look at finding some second hand rotators and see if I can hack something together. On the usual local swop shops I found an old Ham IV azimuth rotator for sale, it was already modified for pc control via RS232. This sorted out the azimuth side of things (or rather so I thought, more on that later). After a bit more asking around I managed to find an old “new” Kenwood kr-500 elevation rotator. Its an old rotator, but it was still new in the box. To be honest I bought a few older rotators as well, but those turned out to be either junk or not viable for what I was planning.
First one on the bench was the Azimuth rotator. Investigating the RS232 mod that a previous ham has installed I realized it had a few flaws. You could send it a “move to” position, but while it was moving to that position it didn’t give feedback, only once it got the destination did it communicate back. I didn’t like that at all. Another issue was that the rotator had a solenoid brake on it, which meant that every time it stopped and started it had to engage and disengage the brake. This is not really a flaw under normal circumstances because it was designed for very big antennas and also you just have it rotate to a certain position and then it would stay there for a while, until you moved it somewhere else. For satellite tracking however your need it to move slow and smooth (and preferably not make a lot of noise while moving). None of the above applied to the current state of the rotator.
At this point I received the Kenwood KR-500 elevation rotator so I decided to get that going first. It was as advertised, a brand new rotator, dusty from sitting on a shelf for years. I had the rotator up and running after some wiring and some new grease in the bearings. It worked well, but it was completely manual. Time to automate it!
I had looked at various options on the internet like the K3NG rotator and the LVB tracker. I found them both unnecessarily complicated but it did give me a few ideas on how to interface to these rotators. Both of my rotators had two switches, to control the two directions and they both had an analog input coming in from rotator to give feedback on where it was. The ham IV also had a switch for to engage/disengage the break.
The simplest solution was an Arduino and two relays. The one relay would enable the power to the switch and the second relay would determine which direction I would turn. This ensures that both directions will never be powered. I’m using an analog input for the feedback. The Arduino get the azimuth/elevation data from an attached computer and then move the rotator to the new position based on the feedback it received.
On the Kenwood this was very easy as the feedback from the rheostat is isolated inside the rotator so I could separate that on the wires coming down and just feed it with 5V to get my analog input.
On the Ham IV this was a bit more complicated as it is grounded to the AC power inside the rotator. Luckily I found this article indicating that it could be isolated inside the rotator with a bit of a hack.
For the Ham VI rotator I also decided to just keep the solenoid powered so that the brake is disengaged. This would allow me to freely rotator the rotator without the pesky brake stopping things and since the brake made a lot of noise it would keep things relatively quiet, especially when trying to use it at 2 in the morning.
Excitedly with that sorted I got some friends over and the following monstrosity went on my roof.
I couldn’t connect the antennas yet as I was still waiting for the coax cable, but atleast I could start playing with the tracking of satellites and work on the control side of things.
Sadly after a day of playing, the azimuth rotator was back on my workbench 🙁
Turns out my idea of just keeping the brake disengaged went south. Keeping it powered for too long destroyed it and in the process engaged the brake. I opened it all up with the idea of fixing/replacing the solenoid, but it seemed a lot easier to just remove the brake plate from the rotator. Noise and brake problem solved. Normally I wouldn’t recommend this, but since the rotator is already overkill for the antennas that I will be using I don’t think this will be a problem. Only time will tell 😉
Throw in a raspberry pi with some Node-Red and I had a fully controllable azimuth/elevation rotator 🙂
Part 2 explains in more details what I did on the software side of this project 🙂