VLF ⁽¹⁰⁾

One of my interests, of which there are far too many for me to ever get anything done, is VLF. I regularly receive the broadcasts from SAQ and having a bit of time after the Christmas holidays and before having to get to grips with the garden ready for spring I downloaded Opera v1.6.5 by EA5HVK of VARA etc. fame. It can be found via https://rosmodem.wordpress.com/ I didn't (yet) find a lot of information but there has been a bit of chatter on the VLF email groups of late and the software basically needed very little setting up - however I am receive only yet so time will tell. Anyway, it installed under Wine on one of the Linux boxes and only offered me the internal soundcard for audio, which is what I needed anyway. The only antenna I have which is suitable for VLF reception is the YouLoop in the loft. This works well with the Airspy HF+ Discovery and SDR++ on the Mac for reception of SAQ and the plethora of 'interesting' signals down there. So I questioned that Opera would work if I simply piped the audio from SDR++ into the Linux PC - it works with…

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

I now have a second YouLoop (supplied by Moonraker) set up in the loft, this time connected to the RSPdx which itself is connected to the Linux PC. I use SDR++ on the Mac and am getting used to the excellent software (see https://www.sdrpp.org). There are versions specifically for Ubuntu, Windows, MacOS (Intel and Apple silicon) and the Raspberry Pi, plus the source code is available to compile yourself. So I wanted to compare the Airspy HF+ Discovery and the RSPdx. When installed on the Linux PC SDR++ does not see the RSPdx. However, once the relevant API is installed and running it duly appears in the devices list as SDRplay and displays the necesary antenna selection menu. So here they both are, looking from 0 to around 85kHz. First the Mac and Airspy: And the Linux PC and RSPdx: This is about as clean as I managed to get the various settings and it is particularly useful having the same software on each machine. Of course this is a rather arbitrary comparison given the multitude of settings and the fact that they are on two different platforms, plus the two YouLoops are facing in different directions. But it does…

Just recently I realised that amongst my kit I do not have a scanner other than the baby IC-R2. So I had a look to see what there is and they range from cheap but limited range ones that do not have a continuous coverage to expensive types that are just way over the top for my needs. My interest is limited to having something I can quickly switch on and listen to a few spot frequencies, including amateur radio ones and the local airport ATIS. I also have a bunch of various SDRs but none met the 'quickly switch on' requirement. Time to fiddle then. Other than the various Raspberry Pi systems the only always-on system I have is a Mac Mini. The other two desktops - Linux and Windows - only get turned on when I want to use the FT450D or TS2000X on digimodes or I need more screen real estate for something. So what can I do with the Mac? I already had CubicSDR loaded and I downloaded the Mac version of gqrx. As I use SDR# on Windows and after reading some blog posts I found and downloaded sdrpp. I already have the Airspy HF+…

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