Antenna Rotator
I've been interested in working satellites recently. In the past I've received SSTV from the ISS with just the rubber ducky antenna on my handheld radio, but transmitting the repeater would be another matter. I also tried a few times to get NOAA weather images, but using a simple 120degree dipole didn't get me anywhere.
I decided to have a search on AliExpress for different options to rotate an antenna. I definitely wanted to be able to change the elevation as well as azimuth, but ended up stumbling across some quite large pan/tilt mounts for security cameras. Sceptically I decided to order one. It worked out roughly £110 shipped to the UK.
The rotator has a built a built in position encoders (pretty sure they're just potentiometers) and accepts commands over RS485, which was a bit new to me. The manual said something about PELCO-D so I tried building some data frames and sending them over to the rotator using a cheap RS485 USB adapter. After figuring out that I needed a terminator and sticking 100 ohms over the data lines, I had it moving. I wrote a small program in Node.js which listens for positioning commands over TCP, just as rotctld does. With a bit of faffing around with calculating angles, I had it tracking satellites from gpredict.
Here's a video of it tracking a NOAA satellite:
and here's an image I managed to get from a NOAA satellite showing a big cloud formation approaching from the west.
I have tall buildings north and south of my house which makes it slightly difficult (impossible) to hear the satellite as it's coming over or approaching the horizon. I start to hear it when it's at around 30 degrees elevation.
The main disadvantage of this rotator is that the tilt rotation is limited to around 28 degrees either way. In order to aim at satellites which are passing over head, I used a vacuum cleaner tube which had a convenient 45 degree angle bend. That means I can do 0 degrees to roughly 80 degrees, which covers most passes.
I still need to build a much better mount for the antenna to the rotator, but I'm also planning to experiment with putting a small dish on it to try and get images from GOES, so it's not a huge concern at the moment. If I do want to improve the mounting, I'll probably have to build or buy some kind of tripod which the rotator can sit on. At the moment it's screwed down to my old dining table, which is quite large and would get in the way of the antenna if it was mounted closer to the rotator.
I've also ordered a GY-521 gyroscope module which I'll hook up to a microcontroller to get more accurate azimuth information. The built in encoders are a bit noisy.
Anyway that's as far as I've gotten so far. While I've heard the repeater aboard the ISS using this setup, I've not setup my radio for the split uplink/downlink. That's something I might try and do soon.
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Comments and feedback are welcome by email (aaron@nospam-aaronsplace.co.uk).