VLF ⁽⁸⁾

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

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.

Another new toy arrived today. A Behringer UMC204HD "2x4, 24-Bit/192 kHz USB audio/MIDI interface". I had been reading about the use of soudcards for VLF reception and the raves about the UMC202HD - the 204 model has the addition of a MIDI interface as well which may be useful and one came up at the right price (ok, I missed several of the 202 models on eBay so grabbed this 204 one buy-it-now!) I did experiment previously with the built-in soundcard on the Linux PC but got very poor results, quite possibly due to a lack of perseverence (fiddling) on my part. Anyway, I took the advice of the many raves. And it works!I installed the excellent vlfrx-tools package plus an additional package vtlivesgram. Running vtcard and vtcat piped into vtlivesgram results in a very useful display: The trace above shows peaks where I see them using the Airspy HF+ Discovery / YouLoop combination which provided my first ever reception of SAQ. The results are limited when compared to the Airspy but that is to be expected. Here, the Behringer input is simply the output from a PA0RDT mini whip in the loft, plugged directly in via a 1/4" jack.