Help debugging station 977

Hello all!

In our attempt to find a better UHF omni-directional reference station setup, I have been testing (in parallel with work that is happening more thoroughly on the satnogs-kit repo) a setup with quality components.

The BOM can be found in this document.

The station seems to be quite deaf and with a higher noise floor compared to what is the comparable setup of station 21. The differences are the RPi (4 vs 3) and the LNA since we dont have access to the novakx LNA that was available on ebay before.

To see the difference you can check some examples of exact same passes here (the stations are 1km apart):

Station 21: https://network.satnogs.org/observations/1177016/
Station 977: https://network.satnogs.org/observations/1177017/

Station 21: https://network.satnogs.org/observations/1170880/
Station 977: https://network.satnogs.org/observations/1170941/

What I have tried on 977 so far:

  1. Play around with gains (higher or lower compared to 21)
  2. Tryout 3 different LNAs (all with and without bandpasses and with comparable gains to the one in 21)
  3. Plug the rtl-sdr while on the antenna, on my laptop and turn on/off the RPi4 (to check for noise) and do the same in all combinations with the LNA power (from RPi4 and from my computer). No difference observed other than 0.5db fluctuations.
  4. Replace the antenna with an eggbeater.

All the above have yield no results.

I also measured with the VNA the turnstile antenna directly (as mounted), and with the cable from the station box to it. The results are as follows:

Without cable:

With cable:

At this point I am suspecting the cable itself (the outside one, since all the internals are brand new from mini-circuits) and will be making a new one and trying it out.

I am obviously missing something here, and would welcome any pointers/suggestions. This is the first time that a station has given me so much trouble :slight_smile: .

2 Likes

Make test without BPF.
This setup: ANT-LNA-SDR

The RTL-SDR dongle could also be faulty. Considering the number of RTL-SDR dongles LSF has bought, you should probably have a handful of bad dongles by now :slight_smile:

I’m not exactly sure about your hardware and test equipment so for what it’s worth this is what I have found on my setup ID-568 & ID-724 by experimenting. The 3rd RPi is for dump1090.

I run 3 raspberry Pi 3+, 24/7. I had S9 noise on my Ft-817 transceiver. Antennas are home brew QFH for 2m & 70cm, an upgrade from home brew eggbeaters with 2 LNA4ALLs at the stacked vertical antennas .

To get rid of the noise, I put all 3 RPis in aluminum cages and made sure the RTL-SDR dongles were earthed as well all to the shack grounding system.
I made sure I bought genuine V3 dongles after buying 2 fakes on fleebay. I got rid of my switched mode power-supplies and build an analog LM338K 5V regulator. Less efficient but no noise.

I left all gains and PPM settings at default. Noise now is S0, no noise.
Check it out for yourself on my satnogs stations.

My 2 cents worth, Bob vk2byf

4 Likes

Already tested, no change :frowning:

Swapped it with a new one. Still no change.