vlfrx-tools ⁽³⁾

Today saw the Christmas 2025 broadcast from SAQ. I set up three receivers to see if any could pick the signal up. These were as follows: YouLoop 1 (loft), Airspy HF+ Discovery, Mac SDR++ YouLoop 2 (loft), Heros VLF converter, SDRPLay RSP2, Linux SDRconnect PA0RDT miniwhip (loft) plus associated preamp, Behringer UMC204HD, Linux VLF-RX tools During the event the VLF-RX code refused to start because, I think anyway ALSA mixer had claimed all the interfaces - the error was that the interface was busy. I was running YouTube on that PC for the live stream. There was no copy, not even a trace of the signal via the RSP2, but the Airspy setup worked fine. Signal strength was well down on last time but still readable visually and audibly although the report I submitted was QSA 2 and QRK 3. The screenshot above shows the reception plus the difference between the LNA being off (lower half) and on. The YouTube video of the event can be found at https://www.youtube.com/watch?v=uSGQ0zR188Q

SAQ was received fine here on the 24th December for their Christmas broadcast at 08:00. This was again using the Airspy HF+ Discover and YouLoop in the loft. I had a bit of time to fiddle with settings in SDR# this time, reducign the bandwidth to 100Hz and trying the HF AGC on and off - leaving it on produces better audio but really not much difference between on and off. The signal from SAQ was showing as -100dBFS vs -110dBFS background. Nothing at all received using vlfrx-tools via the UMC204HD + PA0RDT mini whip. That does show the same large peaks above 19kHz but not the one at about 16.5kHz (see above) nor that smaller peak seen at about 21kHz, so no surprise it did not see SAQ. But never mind, it's still useful. The Youtube recording of the event can be seen at https://www.youtube.com/watch?v=0CQZmW_vE00

Here is a quick and dirty comparison between the Behringer UMC204HD + PA0RDT mini whip and the Airspy HF+ Discovery and YouLoop looking at a similar amount of spectrum from 0 up to 96kHz or so. First the UMC204HD: And the Airspy: This was not done in any scientific fashion, it's just to show that the soundcard method works ok but is not as good as the Airspy. No surprises there and this is no criticism of either method. I can see the utility of the soundcard method when coupled with the vlfrx-tools package as all manner of analyses become possible. I have only just started reading about that.