VLF/LF/MF/HF Active Vertical VLF Performance
Using antenna to feed a SuperSID VLF receiver (part of the Society of Amateur Radio Astronomer's and Stanford SOLAR Center project http://solar-center.stanford.edu/SID/sidmonitor/) and also my KiwiSDR thanks to the provided dual receiver antenna port, which is why I wanted this type of antenna. It works well across the RF spectrum with my KiwiSDR on the SDR.hu network, but I'm just floored with it's VLF performance with the SuperSID! I've attached some screen captures showing the results. I use Spectran to provide a waterfall display and opted for colour and 60 sec screen shots to show the heat/energy signals of the various VLF stations during the course of the day. By using Irfanview I can rapidly flip rapidly through the images and spot any new stations or interesting ionospheric effects. The SuperSID's job is to listen and detect ionospheric disturbances (SIDs) and my and the other SID station's data are streamed to the Stanford server for analysis.
I was surprised that in my city neighbourhood that the only RFI I had to deal with was my Astron switching power supplies running my radio shack gear. It put out a very nasty spike at 30 kHz and I couldn't shift it out of the receivers passband (only a few kHz) so it really desensed the SuperSID but I ran a 15 m length of RG58 up to the kitchen shack and that put enough distance between it and the Astron PS. I may have to look at wrapping the SuperSID (these new ones are built into small shallow tin cans) with mesh to act as a Faraday cage and see how that works.
The lower end of VLF below 10 kHz shows all the lightning activity that generates a lot of interesting things that you can also study and record. There's a receiver dedicated to that as well, but it's a kit so not everyone feels like building kits these days for some reason http://theinspireproject.org/default.asp?contentID=3. In this case you can get buy with just a 2 m whip attached to the receiver (designed to be portable).
I haven't had time to wind the suggested 1 m box magnetic loop yet to run A/B antenna comparisons but I think that an active antenna design should do a bit better than a passive one. I also thought that the vertical antenna would pick up a lot of noise on VLF but it seems to be doing a very nice job.
For those who want to check out VLF you can use my KiwiSDR albeit there's a 2 second/processing delay with the KiwiSDR and then Spectran has a slight processing delay to. It's only a problem with FT8 and the fast turn around digital modes if you use say WJST-X for decoding.