Things made with bits and soldering irons
I finally got a decent image from the space station. The recent ISS passes have been plagued with interference from somewhere, but this image seems fine.
I’m using this setup — the aerial is my Cebik Moxon.
The Raspberry Pi 3B plus is running QSSTV. The USB Audio dongle is a 33051D. The pre-amp is an M-100.
I use a Yaesu FT-60 for my satellite radio. It’s a little onerous to manually program satellites into it so I use the CHIRP application to do the programming.
I can’t use my FT-60 programming cable directly on macOS (my native OS) because it has a Prolific chipset for USB/serial operation and its driver clashes with the FTDI chipset which is in other USB/serial devices I use.
I first used a Windows 10 virtual machine (VM) under VirtualBox to run CHIRP. This worked fine. But I only use Windows 10 sporadically and when I start Windows 10 it nearly always wants to reboot to do an update. This is tedious and slows things down a lot. I spent more time waiting for Windows to update than running CHIRP.
So I’ve put a Ubuntu VM onto VirtualBox and now run CHIRP quite happily from there. Hopefully Ubuntu won’t insist on upgrading quite so often as Windows 10 does.
I decided to build or buy a diplexer to communicate with LEO (low earth orbit) satellites that use cross-band operation.
Some of the satellites in LEO are U/V or V/U. U/V means the satellite receives at UHF but transmits at VHF. V/U is the other way around.
My space aerials are in the attic and there are only two cables going from the shack to the attic. One thick cable is used solely for HF, and the other thinner cable is used for higher bands, 6m, 2m and 70cm.
A diplexer allows the use of different frequencies on the same cable. In this case it allows both VHF and UHF aerials to be used on the same cable. The diplexer has one input (from the transceiver) and two outputs (one to the VHF aerial and one to the UHF aerial) when transmitting. The diplexer blocks VHF signals going to the UHF output, and also blocks UHF signals going to the VHF output. In this way the transmit power goes where it is most wanted, that is, to the appropriate aerial.
On receive the same ports are used but there are two inputs (one from each aerial) and one output (to the transceiver).
I decided not to built a diplexer for VHF/UHF operation as fiddling with inductors at those frequencies can be a bit hit-or-miss unless you use SMD components. It’s much easier to buy one, especially for those of us who are challenged when building VHF and UHF inductors. There are a few diplexers on offer, and I chose one on eBay from HA8LFK. It seems well built and works fine. The 50W limit certainly won’t affect me just now as the highest power I can send on VHF/UHF is 5W. One drawback may be that the sockets are SMA and my shack mostly uses BNC for VHF and above.
I have characterised this diplexer by sending sine waves of various frequencies through its transmit path and measuring the outputs. The signals came from my WaveTek model 1062 sweep generator and were measured at my HP 54615B scope. I used SMA/BNC adapters and short BNC cables to connect the diplexer to the test equipment.
As you can see the sweep generator signal is almost flat. The VHF port peaks a little lower than the 2m band. The UHF port peaks a little lower than the UHF band. Neither seems significant.
The insertion loss on transmit is 1.45dB at 2m, and 1.79dB at 70cm.
I didn’t make a graph for receive but did measure the insertion losses: 0.72dB at 2m, and 1.24dB at 70cm. This surprised me as I would have thought the diplexer would be symmetric, but it appears not.
Now to use it in anger …
The International Space Station transmitted some slow-scan TV images during February 2019. My 2m Cebik Moxon in the attic was easily able to receive these images even at quite low elevations. No need to be outside pointing a Yagi in the February chill!
The images I received can be seen in the ARISS SSTV Gallery. You’ll need to put in my callsign: MM0GYG.
They handed out awards too.
Great fun!