SNR of the CW beacon

  • I had a CW filter switched in on SDR console so the G4JNT s/w wasn't getting the full picture, now with a 2.8kHz SSB filter, settings as per DB8TF's and Peak -> CF and tracked I'm getting 51dB and 17dB.

  • I have just realigned my 1.1M dish after storm Hannah blew through yesterday. When I say re-aligned, I mean re-mounted after an incident during the re-alignment (not related to the storm), but after it popped out the mount, I decided to remount on a smaller diameter pole to reduce a slant on the dish that I had.

    Long story short:

    1.1M Dish, Beacons 19-20dB above the noise floor, *BUT* in 500kHz B/W, gnuradio, USRP N200, Still need to tweak dish illumination and LNB skew

  • there are many hints regarding bandwith and so on, but I'm not sure if this is just a math issue.

    Because the CW beacon (in the steady phase) is just one single frequency, I do the measurement by comparing the spectrum to a known source.

    First I connect a signal generator (single frequency as the beacon) and write down the dBm value for each dB-Line of the SDR software (I don't take care on the labeling of the spectrum's y-axis).

    Then I connect the LNB and read the noise level as well as the beacon level and look into this calibration table for the real value. This makes the measurement almost independent of the SDR software.

    To be honest, I have no idea if this is a good procedure or just nonsense, but it looks to work well. The CW beacon is abt. 28 to 32 dB above noise level.

  • om0aao please check on my post about the SDR-Console readings.. They are pretty hard to interpret as the signal history is displaying peak and not average.. and the Noise BW of the FFT is not straight forward to see. So it's hard to compare.

  • Thanks, Achim DH2VA ! But I am afraid that I am not very far from the real. I use signal strengh window which is showing maybe each second avg.signal strenght. First I tune on the beacon frequency, then few kHz away in free space.

    I have second LNB (uknown) so maybe I can try it with it. I think there can be difference, too.

  • om0aao if you really want to use SDR-console, please switch on the FFT statistics. This will include the FFT Bin size in the display. see here

    signal history shows =- 75.8 dBm which is matching the y-axis at the left side for the peak signal. Note the Resolution which is 19 Hz, this is the FFT bin size.

    Now I set the receiver in noise. The signal history shows -103.6 but if you look left, this is hardly the average noise power. The average is probably something like -111 dBm. So -75.8-(-111) = 35.xx dB in a 19 Hz bandwidth (this is the noise BW). 19 Hz is (almost) 13 dB more than 1Hz so this is then something around 48 dB in 1 Hz. Which for me is close enough to the 50-53 dB (1 Hz) noted in this thread. After all, this was eyeballed.. :)