Thanks for the plenty input!
Did you reposition your GPS antenna? Where is your antenna located? Indoors? Can you try a different GPS antenna?
Yes, I have re-positioned it. Originally it was inside directly behind the glass. I have put it outside and tilted it a bit. The signal seems to get more stable. But still not really reliable. Which is odd because I am at the top floor of the highest building in the area. I get between 4 and 7 satellites.
Do you have any suggestions what GPS antenna would be a good choice?
Please name the brand and model of your lnb.
The unmodified LNB is a "LNB 1" digital single LNB by SCHWAIGER. Pretty standard with an LO of 9.75/10.6 GHz.
How do you feed the reference from V3D to your modified lnb? The reference is on the wideband connector only, not on the NB-Connector. So if your lnb shares output and reference input on a single connector, you need to rethink the setup.
I have two coax connections between mod. LNB and Down Converter. One for the NB and one for the WB+Reference.
Had same effects with somtime GPS loss ... , mostly after new start of the converter.
I changed the GPS Antenna, now without problem ...
Maybe a try?
73 de Robert
Good Idea. May I ask which antenna you use?
I promised you screenshots of the Gqrx:
This is what I get with the bias tee and the unmodified LNB.
This is the result when I use the modified LNB and the Down Converter. (Even when the display shows everything should be alright GPS wise.)
I tried to measure the frequency on the GPS module but I wasn't getting anything that looked like a proper clock. I have to measure between GND (Pin 2) and Debug Output (Pin 4), right?
I am not sure if I used the Oscilloscope correctly.
I also made a very strange observation with the 40 MHz out put. When the display showed GPS running the frequency was not correct:
But a few minutes later it was the other way round:
Do you have any Idea what this could mean?
Thank you very much for your patience!