I have increased the gain a little on my ID 568 and ID 724. It seems like a better result. How will I see if I have gone too far with the gain? I’m on 33.8 with masthead preamp and QFH antennas at the moment. I also see some Doppler shift on some observations. Did I miss a setting somewhere in my satnogs-setup? Does the software look after that automatically?
Thanks
You will start to see more spurs and aliasing that looks like terrestrial signals but usually are from within or close the sdr.
Taking obs 11982722 for example, you will also see saturation of the sdr from the strong signals, these show up as horizontal patterns aligning with strong signals from the satellites.
This can also be the case if you have a big directional antenna pointing to a strong transmitter, but for omnis this is less likely and too high gain is more probable.
Using the rising noise floor method is a pretty good start. Giving that 10-20dB extra will often get you in the too high region.
This is automatically tracked and based on the TLE and local time on your station. Having the clock automatically adjusted with ntpd or similar solves one of these. The TLE’s might be outdated, or the spacecraft might have done a correction to it’s orbit.
Do you have a example in mind ?
Thanks for your reply David. I am familiar with the rising noise floor method to determine gain settings. I do this with my SDRplay system in real time, but how do I do it with SatNOGS observations where I have to guess a setting, then wait for some observations and try another gain figure. Very slow trial and error.
I can’t remember the suspected Doppler observation. Basically I had 3 data bursts which started from the top waterfall centre. The next one was a little to the left, and the third one was more to the left. Not a problem, just curious. Re observation 11982722, the faint horizontal lines either side of the main signal, is that caused by too high a gain setting? Thanks for your help.
Bob
Bob,
The way I set my gains for SatNOGS is to use the existing SatNOGS hardware setup, but with a RPI image that has a SDR program that can work with your particular SDR.
Basically I pop out the SatNOGS SD Card and put in one with GQRX on it. You need a temporary screen and KB/Mouse……Then simply use the rising noise floor method to get the gain. Once you have that change back to the SatNOGS SD card and set the gain.
For simplicity I use a RPI image that was created by Luigi Cruz. It has a bunch of ham related programs including GQRX and it seems to work with most of the common SDR’s. Dragon OS is a newer RPI image that also has a lot of ham radio software.
If you want to avoid the screen/KB/mouse issue you could try one of the VNC programs.
I use GQRX rather than other SDR programs because I believe it is based on the same basic GNU Radio framework SatNOGS uses….although GQRX is an older program so that may not be entirely valid now days, given the more recent developments with GNU Radio.
Anyway it works for me.
Hope this helps.
John VK4JBE
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