Active Antenna EU - a pretty good performer for RX

Popoutman

In the past week I finally took delivery of my newest attempt to get good consistent receive capability in a small space., and it's a pretty good performer.

I ordered an Active Amplifier Antenna (AAA-1c) from http://active-antenna.eu/. While I was waiting for it to arrive, I got myself two 3m lengths of 20mm diameter AquaStec aluminium/plastic composite piping to act as the antenna loops, and I got 20m of FTP (foil twisted pair) Cat6 cable.

Upon arrival, I bent the loops into circles, scraped the plastic from the ends down to the aluminium and bolted short bolts through that, giving a nice low impedance electrical connection. Both loops were wired to the amplifier box. The FTP cable was attached, the control switch cables were attached, and it was powered on, and I was pretty amazed by the performance of this from inside an apartment building.

I'm currently in Switzerland, staying with friends in their top floor penthouse type apartment for a few months while on contract here. I've got the loops laying vertically against the internal side of the roof angle, at about 25m AGL, in the same plane, looks like an infinity symbol. I'm not going to get to mount this antenna outside on the balcony, but I don't really need to.

I can get BBC radio 4 about as clear as I could from the West of Ireland, and Shannon Volmet on 5505 comes through at about 40dB over the noise floor. The best I had been able to achieve in the MidWest had been about 30dB with a 20m randomwire.

I'm seeing what I think are Alpha transmissions on the VLF side, the 60kHz time signal is clear and strong, I'm seeing NDBs at nighttime of hundreds of kilometres away, and all the way up through the spectrum I'm getting to see faint signals. BBC World from Ascension is very clear, I'm getting faint FM signals as well. The broadband characteristics are impressive.

I'm using a variety of SDR hardware and my laptop to hear what's going on, using any of an Airspy R2/Mini/HF+Discovery, or an SDRPlay RSP1a.

If I get a chance to get maybe another of these antenna (or maybe three antenna and set up phased array..) set up if I end up back in Ireland on the KiwiSDR, it will make a huge difference.

I can heartily recommend the AAA-1C antenna. It's showing great broadband characteristics, the flexibility of the choice of loop configurations will mena something for everyone, and the ability to add a few of these antenna to become a nice phased array is an added bonus for the hardware tinkerers out there. Add to all this that it's as unobtrusive as you'd like, if you choose a nice colour of pipe you should be able to get it to blend in.

It makes a *really* good match for the likes of a KiwiSDR, and I'm having fun setting up that combination in Zurich.

Really happy, and under a hundred yoyo too all in for the kit and the loops..

deaglan169

Hi great review and info i was going to purchase this amplifier kit and make loops similar to yourself but couldnt find any decent reviews so went with a wellbrook, did you mount the 2 loops at 90 degrees to each other?

Popoutman

I'm trying out a few different configurations every so often.
I'm using a second KiwiSDR as the receiver, with a nearby Pi4 running a few wsprdaemon listeners, and using the output from those to get noise levels over time.

I don't have external capability for this antenna yet, so things are being set up in an attic space at the top of the ~6-story apartment building here.
I've tried the loops nested at 90 degrees apart, side-by-side with both orientation of loop 'B', and the current one is loops in parallel with the direction of the loops being opposing. That one is the best currently as it nulls a major noise source for me and effectively lowers the noise floor by a significant margin. At some stage over the Christmas season, I'll pick up a length of wood and another pair of waterpipes, and I'll do a vertical config, each side at 90 to the other, and a pair of parallel loops tied together.

Strangely enough, though I appear to have decently low noise levels, and apparently good signals, I'm still getting about half of the reports that I am from my KiwiSDR in the MidWest. I'm hearing 9-10% of all worldwide wspr transmission here in Zurich, and the MidWest one is hearing 15-20% of all wspr transmissions.

The ideal end game antenna config for me will be quad loops, each lobe with a parallel loop for the lowered inductance, all mounted i one plane on some form of rotator. I just haven't gotten around to sourcing the bits for it yet.

Popoutman

I recently added a second pair of 3m pipes, and added the loops in parallel. As the attic space where I have the antenna located is rather small, I've got the four loops in the same plane, with what would be the "upper" pair of loops on the south side, and the "lower" pair of loops on the northern side. I remembered to twist together the wires between the loops ends and the receiver - bell wire would have been perfect to carry the signal.
I did notice a difference in the behaviour of the antenna depending on which way the loops were oriented with respect to each other. If the "+" were all on the same side I got worse behaviour than if I had the "+" on the upper side matching the "-" on the lower side. I suppose that's why it's called crossed parallel loops..

Noise levels are reasonable for a city location. I have a bit of background RFI from 0 to 2MHz with noise floor between -80 and -90dB and SNR of 50dB for best MW radio signals at night. There's thankfully wonderfully low noise floors (-100dB) from 2MHz to 10MHz, a little bit of noise (-80 to -90 noise floor again) from there to 18MHz and a little too much noise for my liking from 18MHz to 30MHz (-67 to -78 noise floor). Thankfully with the current propagation conditions there's not as much of interest up there, and I suspect that a lot of the noise is outside of my control anyway.
With the second loops in parallel and using in the crossed loop configuration, I'm definitely getting better WSPR reports. I suspect, though I haven't properly calculated this out, that with the additional loops and a better orientation to null local noise, I'm getting about 6dB better SNR for WSPR. Comparing to before Christmas, I'm getting to about 12% of global WSPR transmitters compared to ~8% in November.

I've also added splitters to allow decent signal to get to a pair of RPis that I have running SpyServer, with an Airspy/Spyverter combination on one and an HF+ Discovery on the other. Pretty cool to be able to see a signal on the Kiwi, and then really zone in with the HF+ and get a better copy of the signal that way.

Hmm, that reminds me, I must take a look at the BeagleBone AI as a possible upgrade for one of the Kiwis if/when next move takes place.

My next improvements to the antenna will have to wait until a new apartment for space reasons. I will however rig up switches instead of the current winding together of bare cables, for the selection of the desired antenna mode. Eventually I will do the control via serial port, and control with RPi or the Kiwi antenna plugin.