Friday 1 July 2022

HF Airspy Mini + Spyverter + Random Long Wire


Hey you. Look what I got. Thats right, I got an airspy mini & spyverter :)

I have had the airspy mini for a while now, I use it for listening to satellite communications. It seems to be my go to SDR, having also a RTL-SDR and an SDRplay RSP1. I won't go into reasons why it is my go to more than that it is more able to pick up signals and is more user friendly with my computer, and has bias tee.

my rtl sdr HF usb dongle - beginner level on HF?

I wanted to see if I can extend it's capabilities to using HF bands (0-30Mhz) just to be able to explore RF and learn a bit more. I tried with my RTL SDR HF dongle which gives basic results (0-14Mhz) but lacks bias tee and has EMF noise in the waterfall, the SDRplay has good potential but it is so terrible at integrating with SDR# or SDR++ on Linux or Mac it is just not worth going down the Rabbit Hole; if this issue is sorted then I might come back to SDRplay.

So, I bought myself an Airspy Spyverter last week and here are my first impressions. I bought all devices myself and I am not doing paid promotions or product endorsements.

Firstly, the Airspy and Spyverter do not come with a printed manual, so you must research ho to hook it all up correctly or else you could damage the devices. I connected my Airspy Mini & Spyverter up like this:

note the position of the micro usb socket on the spyverter. It helps to know this for orientation. Also it is suggested not to connect usb power to it while at the same time using bias tee power, as it might cause damage.

I get it connected like this:

I stuck on the self adhesive heat sinks to the airspy mini as i was worried about the amount of heat it produces - I am told on forums that the very high heat is a normal feature of airspy mini, similar to the heat produced from running Jetson nano's, Raspberry pi 3's or 4's wihout heatsinks or fans attached.

My antenna for basic first time HF reception is a random long wire antenna connected to a 9:1 unun. I use over 16m of wire for the main element, and a few metres of wire going to a grounding source which is supposed to reduce electrical noise. in between I use a self-made unun/balun using a ferrite ring, wire, and connectors housed in a plastie box:

my homemade 9:1 unun/balun

And so onto the results of the Airspy mini + Spyverter HF combo. Am I pleased?

Well, it's a mixed bag. I am only a week or so into using it so perhaps I have not got the setup creases smoothed out yet. 

Things I like about AirSpy Mini + Spyverter:
1 - this combination gives me the HF 1-30Mhz I was looking for (the rtl-sdr only does 0-14Mhz HF).
2 - the gain controls seem to actually have an effect on signal performance.
3 - it is more straight-forward to get up and running receiving signals.
4 - it has bias tee power.
5 - I am definitely getting more radio stations than I did with either RTL-SDR HF dongle or RSP1 dongle.
6 - The stations I get are more clearer than when using either two other dongles.
7 - using the Airspy Mini + Spyverter with SDR# software, it is the best combination I have used to fine-tune audio and noise reduction to achieve clear speech even in high static, faint HF radio stations. It almost seems like a magic trick sometimes.

Things I am yet unsure about Airspy Mini + Spyverter:

1 - Is my location in the centre of a busy built up urban area causing me to pick up more EMF and RF noise using the more sensitive Airspy mini?
2 - What is causing the different wave pattern in the SDR software?
3 - Is my antenna sub-par?

Using the various SDR devices I own, they all produce different and varying outcomes on the RF waterfall of various SDR computer software. As a mostly MacOS user I have used GQRX, CubicSDR, SDR#, and SDR++.

I tend to use different software packages mostly because as yet, I haven't been able to find a one-for-all complete software package yet. SDRplay devices are the big stumbling block here. My RSP1 I can only get working using CubicSDR on Mac or SDRuno or SDR# on Windows 7/10. I  very rarely use my RSP1 maybe once a month I take it out the box, and that is just to compare against other devices.

SDR++ comes close to being the most one-for-all complete package, but as yet, it does not have the magic audio processing that SDR# has. And as you may realise, SDR# is a Windows only package. Having a Mac version would be tremendous. Many people would be happy.

So onto my signal tests.

Using my Airspy Mini + Spyverter combination, it does undoubtedly produce lots more radio stations and listenable signals for me than my other devices. It is as simple as that.

However I am now contending with some other things which I want to know more about and try to find solutions for.

Mostly. What is causing these RF peaks?

When I read up on HF sdr, I saw waterfalls which looked like this:

Nice, flat spectrum, with nice clear well-defined station peaks. 

Using my Airspy mini + Spyverter setup I get this:

I get the nice clear well-defined station peaks. But I also get this huge fat arch of doom. Why do I get this? What is causing it? Why! Why! Why! My life!

I don't get this result using RTL SDR HF dongle, but I also get fewer clear stations. Here is my result using RTL-SDR HF dongle:


Is it because the Airspy mini or Spyverter is damaged?
Is it because the Airspy mini and Spyverter are more sensitive to ALL RF signals including noise?
Is it because of my long wire antenna?
Is it because of my location and my antenna position (in the attic of my end terrace urban house)?

I can reduce this mound by reducing the airspy mini gain to level zero or 1, but also I reduce the clear stations too, they are synchronous:

Airspy Mini + Spyverter set to Linear gain level 16:

 Airspy Mini + Spyverter set to Linear gain level 8:

RTL SDR HF Dongle set to max gain level 49dbi:

Using Airspy min + Spyverter this mound also exists all through the HF reception, an example at 7Mhz is here:

I have tried to correct using:
- Ferrite chokes on the wires - no noticeable difference

- Testing on a different computer, a laptop:

Laptop - Airspy Mini + Spyverter + Long Wire antenna set to Linear gain level 16: 

 Laptop - Airspy Mini + Spyverter + Long Wire antenna set to Linear gain level 8:

 It seems to be a different RF noise pattern than with Desktop computer. So what now?

- Testing with a different antenna:

I try also using a simple telescopic antenna with 'First test' Desktop like this:

Airspy Mini + Spyverter set to Linear gain level 16 (using simple telescopic antenna): 


It looks like the RF noise 'Desktop' mound is gone, but I think it is because the antenna is simple, it is not picking up stations as good perhaps less sensitive? It is similar to Airspy Mini + Spyverter set to Linear gain level 2 or less.

But because my RTL-SDR HF dongle at full gain is not making this, then it could be assumed that it is something to do with the Airspy mini + Spyverter combination? or Long wire Unun Antenna? What next?

It seems that with the Airspy mini + Spyverter combination it is much more sensitive to RF noise from various things perhaps?

So what next?

Further tests:
- Testing outside far away from the house.
- Testing using laptop on battery power instead of AC power adapter.
- Testing using a antenna far away from house.
- Somehow shielding from RF the Airspy mini more? Or is the noise coming from USB computer?

Will update soon.

1 comment:

Sean - G4UCJ said...

Hi, I've just come across your blog, and as you have had zero comments, I would like to give you some ideas.
The first one, looking at your configuration the thing that strikes me is that you do NOT have the bias-tee box ticked. When you use the Spyverter, the bias tee must be ticked, unless you are powering it externally. Once you tick the Bias Tee box, I think things will look much different. A random wire is the classic 'go to' general-purpose antenna for MF/HF. They do pick up a fair amount of noise, especially on the coax feeder from the balun/unun. To improve things, you need to make a common mode choke. Easy to do: Firstly, you need a ferrite core - something like an FT240-43 or FT-240-31. Those are large enough for you to wrap enough turns of coax through. If your noise level is particularly high, you'll need two of them, one at the antenna feed point (just below the un-un) and one just before the coax enters the shack. That should pretty much eliminate common mode currents on the feeder and will reduce your overall noise level. I have an Airspy R2, Spyverter (the original, not the improved version); also have the Airspy HF.+ dual port and HF+ discovery SDRs (which are fantastic HF (and 4m/2m) receivers. I can't compare it to an SDR Play as that is one I don't own (yet). I have a few other SDR's around, like a couple of RTL dongles, a FunCube dongle Pro+ and an SDR-IQ so am pretty familiar with what to expect from them. Looking at your configuration, you have the gain set nice and low, it is possible to overload the Airspy/Spyverter which will result in the screen becoming a mess and the noise level really high. Increase the gain from zero, until the noise floor suddenly jumps right up, then back it off one or two units. That should give you optimum gain and dynamic range. If you haven't already, try clicking the 'bias tee' box, otherwise the converter will not be getting any power and it may look like you are tuned to HF, you won't be and are likely picking up computer/USB bus noise, which is what you can see on your screen. If you need further help, I am happy to give it a go and see if we can get you working properly. 73 and happy SDRing!, Sean - G4UCJ (SWL since age 7, radio amateur licensee since age 14).