I am planning on setting up my first station when spring hits. I currently have a APRS SatGate and want the SatNOGs station to share the 2m antenna.
I have attached a drawing on what I am thinking. Here are my questions:
Will this work?
Any recommendations on a Transmit/SDR Switch? I am not handy (only one arms works properly) so a home made solution maybe beyond my dexterity.
Since the SatNOGs software will be receiving all signals, what is the best way for the SatNOGs software to send the data to direwolf? I found a code snippet at SatNOGS APRS SatGate · GitHub that might work but it is 5 years old. I don’t think both SatNogs and Direwolf can share the dongle.
I am currently running Ubuntu 20.04 on the server and have the capability to run VMs.
First off, the LNA does not sit in front of the SDR but as close to the antenna as possible. Feeding it bias is trickier as the DC path through the diplexer is usually on the low frequency port.
Transmitting close to the station will almost always make any SDR deaf, so it will be visible in the observations quite clearly. Possible, yes.
3.a Regarding the modification of the flowgraps, a variant of this is implemented these days. It is doppler corrected for the sat it is currently observing. Also it’s not short format but float. direwolf needs to be configured to read this. I’m not sure what it can handle, but you need to do the fm (quadrature) demod on the udp stream. The actual sample rate also needs to be guesstimated by one of my scripts. It will also not work when listening on a sat that is not on the aprs frequency.
3.b There is a possibility to run the aprs with the sdr between observations. This is basically what we have done with the bandscan script, check the satnogs-pre/-post for how this works.
The diplex bias feed-through is just a small obstacle, it can be solved in a few different ways, modification of the diplexer itself probably cleanest. I do run this on my station and I built it for wide band reception for multiple sdr’s.
I can absolutely agree that 2 antennas and 2 sdr’s is the simpler method and a lot less hassle, what ‘most’ are using I don’t know.