AirSpy Mini - Initial Impression and mini-review

Medium & long wave receiver discussion
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daveB
Posts: 997
Joined: 07 Oct 2014 16:49

AirSpy Mini - Initial Impression and mini-review

Post by daveB » 24 Jun 2016 17:50

It arrived today! Everything was set up ready to go on the SDR# Build 1444 and it really was a case of 'plug-and-play'. In summary - I'm very pleased with it.

The comparison is with an SDRPlay running on SDR# build 1361 and with a Yamaha TX-930 with 2 x 150 kHz filters and 2 x 110 kHz filters. Both SDRs are set to 130 KHz bandwidth.

In one test the signal has gone through a 12dB low noise aerial pre-amp about 5m from the 2 way splitter to the AirSpy mini and one or other of the SDRPlay or Yamaha TX-930.

In another test - using a vertical aerial - there is no pre-amp before the splitter and a comparison between the AirSpy mini and the Yamaha shows no definite difference. Depending on the station chosen the bit error on RDS can be slightly better or slightly worse on the Airspy mini - than the Yamaha TX-930. This suggests that in my location any sensitivity differences make no practical difference. I haven't done an SDRPlay to AirSpy mini comparison using the vertical as I would have to do a lot of messing about with aerial leads.

An SDRPlay to Yamaha comparison on the unamplified aerial, on the other hand tends to show an improvement in the ber when the LNA in the SDRPlay is on eg BBC R2 on 88.1 is giving around 90-95% ber on the SDRPlay when the Yamaha is only showing a pi code with no sync. Turn the LNA off and both receivers are managing to hold the pi code steadily.

The bottom line is - I can't say one SDR is better than the other (at my location) and are possibly better than the Yamaha. You can overload both the SDRPlay and the AirSpy Mini by whacking up the gain control too high. But backing off to just before this point and reception sensitivity is 'the same' as the analogue tuner (where you have no scope to adjust gain settings).

For anyone who wants to know how much better the AirSpy Mini is to an RTL dongle. Here is a simple indication. I have to fit a double notch filter to the East facing aerial to remove Heart on 102.8 MHz otherwise I have to pull back the gain on the RTL dongle so far it is deaf, to avoid total overload. No worries about this with the AirSpy Mini and the cheap dongle would be unusable on the main rotatable array.

With regard to gain settings the app now gives you three choices of gain control - sensitivity, linearity, and free. When you choose the latter you then have access to sliders for IF Gain, Mixer Gain, and LNA. Personally after an initial play about I'm leaving it on "linearity" setting with a gain between 11 and 13. I checked for images around 85 MHz and adjusted until the one that showed had dropped near to the noise.

Now the AirSpy Mini is supposed to be 6 MSPS and 3 MSPS sampling rate - but the recent review in rtl-sdr.com revealed a way to change the config file to allow 10 MSPS sampling. The downside is more spurii - but none were evident in the FM Band to my eyes. Playing back a "10 MHz" bandwidth gave just over 9 MHz of useable spectrum - which is the whole of the OIRT band including R2 sound. I had no problems with stuttering etc at 10 MHz sample rate as has been reported by some users.

There are a couple of other apps now included. The one of most interest to me is "Spectrum Viewer" this can show various bandwidths from 20 MHz to 1 GHz wide - so at 20 MHz it can show the whole of the FM Band - or at 50 MHz will cover 48 - 98 MHz - so with the right aerial and set up you get early warning of all the SpE. At 50 MHz b/w it refreshes roughly every second. Of course it's SDR# OR Spectrum View.

One point of slight concern - but it is mentioned by AirSpy - it gets quite hot - so mustn't be covered. I'll probably look for a clamp on heat-sink for the long term.

So should you buy an SDRPlay or an AirSpy mini? It has to be said that SDR# is the most advanced 'free' SDR software package compared to others, but HDSDR does a good job with SDRPlay - and you can always play back HDSDR wav files of less than 4Gb on SDR# with File Player.

AirSpy needs an external converter for HF - which I would find a nuisance to have to screw/unscrew every time I wanted to go from HF to VHF - but a) I hardly use HF and b) I've got an SRPlay as well :lol:

So I'm firmly sat on the fence! But having one of each I've got the best of both worlds.

David
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

daveB
Posts: 997
Joined: 07 Oct 2014 16:49

Re: AirSpy Mini - Initial Impression and mini-review

Post by daveB » 24 Jun 2016 23:43

ADDED: I did further testing for the presence of images caused by the low IF architecture. I managed to find a few from the strongest local stations - all but one was weak. This is comparable to the issue with zero-IF images showing up on SDRPlay due to I/Q imbalance, which is not completely eliminated by the API or in SDR# build 1361 by the auto-correction. My feeling is that the AirSpy is slightly better - but you can get better suppression of unwanted images if you run SDRPlay on HDSDR.

It is a matter of trades offs - in my location I'm more likely to lose weak exotic DX under tropo than under an image, as the images from the strong local stations generally fall on a channel which is already occupied.

David

Note: AirSpy Mini: At 6 MSPS a weak image will show up at +/- 6 MHz some 55dB lower in strength than the original signal. On SDR Play an image will show up the opposite side of the centre frequency, so you could have a strong signal 2 MHz below the centre frequency and then find it's image 2 MHz above the centre frequency. Easy to tell if swap I/Q and can hear the same station much more weakly.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

daveB
Posts: 997
Joined: 07 Oct 2014 16:49

Re: AirSpy Mini - Initial Impression and mini-review

Post by daveB » 29 Nov 2016 21:53

I ought to update this as SDRSharp has released some updates to SDR# that have had a big impact on the high side IF image. When you use decimation there is no sign of it!. So with 10 mbps sample rate and a decimation of 2 you get 5 MHz bandwidth - or 4.5 MHz useable when recording.

Unless I'm actually doing a wideband recording I have no problem with using 5 MHz. You can 'fudge' the Airspy mini to run 10 mbps - but to avoid it running too hot I've strapped a double set of small heatsinks to it.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

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