I am considering investing in an Airspy Mini and RPi4. The Airspy Mini would be used with either a Uputronics Saw Filtered Preamp or RTL Triple filtered 1090 LNA (I have both). I’ve read through the various postings about the Airspy Mini and find the views quite mixed. I’d be grateful for an idea of what I could expect to gain from such an investment compared with my current setups. I’m currently using two setups: RPi3 + FA Prostick Plus and RPi3 + RTL-SDR V£ + 1090 Triple filtered. Both are connected to external antenna on the roof.
I changed from an rtl-sdr.com v2 dongle and LNA to an airspy mini. Here is a like for like comparison of the difference between the two when I had my antenna mounted in the loft - There’s about 2 months of rtl dongle data and about a month of airspy before I moved the antenna:
Blue is airspy, red is the rtl dongle. The only difference is the receiver - the same antenna, LNA and coax was used. You can see that there was a very large increase in received messages and the number of aircraft seen as well as a significant increase in maximum range. This is also prior to the improvements made to the airspy decoder later that year.
The airspy is using a pi 4, whereas the rtl dongle was connected to a pi 2, but that doesn’t affect the results really - the pi 2 was easily capable of running the dump1090 decoder and the pi 4 gave no performance advantage. The pi 4 allows running the airspy at 20MHz sample rate which does provide a boost however.
Here is the difference between the rtl-sdr dongle and the airspy with improved decoder and the antenna moved to the chimney - note that the rtl dongle data is from the summer when it’s normally much busier, with the airspy data covering winter scheduling from mid-September until just before the covid lockdown in 2020.
A well optimised rtl dongle will see a maximum message rate of around 1800/s, with a maximum number of visible aircraft around 275. The airspy mini will see a maximum of around 3100 messages a second and easily over 400 visible aircraft. I think @keithma has had over 500 briefly during a period of tropo ducting.
Obviously these figures are prior to covid, so numbers are substantially down on these at the moment.
I think an airspy mini is a pretty decent upgrade - you get performance which is on par with a dedicated receiver like a mode-s beast or radarcape (they may be slightly better, but not much) at a fraction of the cost of those receivers. Getting your antenna up in clear air is by far the most cost effective change you can make if you haven’t done it already though.
Many thanks for a really useful and helpful reply. I currently have RPi3Bs. From your comment about the Pi4 giving no performance advantage apart from allowing the 20MHz sampling rate, would a Pi3b be adequate enough to use with the Airspy? That would save a bit on the cost.
I started with a good Omni antenna well placed on the roof with nearly unobstructed horizon view. All my radio variants had that constant RF input. A dense urban radio environment with high out of band signal levels challenges the receiver.
My first receiver was the filtered FA dongle and a Pi ZeroW. Not very impressive. The processor was limiting performance.
Then I used the same filtered dongle with a Pi 3B. Max message rate was around 800 per second.
Next an AirSpy mini replaced the SDR dongle. The AirSpy’s lower gain required an LNA. I first used a Flightaware filter. Later on I added a low loss cavity filter before the LNA.
Then I replaced the Pi 3B with a 4.
Next I moved the filter and LNA to the base of the antenna to improve SNR.
At the end of all that, in pre-CoVid airline traffic days, the system was reading a peak of 1800-2000 messages per second from 350 - 400 aircraft.
As for maximum range — that never varied much, with even the Pi Zero system detecting high-altitude craft at 200-220 nautical miles.
The AirSpy + Pi 4 decodes many more messages and somewhat more aircraft but at no greater maximum range.
As others have said, the transponder signals tend to be horizon or obstruction limited, not SNR limited.
There is no performance advantage using a pi 4 over a pi 3 if you are using an rtl-dongle. A pi 3 will definitely run an airspy with decent results and much better than an rtl dongle. You won’t necessarily see more aircraft by running at 20MHz, but you will decode more messages. The pi 3 is really marginal if you run the airspy at 20MHz and if you live somewhere that sees a lot of traffic it probably won’t cope with it.
The other advantage of the pi 4 is it can supply more power over USB which can sometimes help with stability.
The airspy does benefit a lot from having a good LNA - I use the rtl-sdr one which I have mounted just under the antenna.
That’s exactly correct! I was running the Airspy Mini with a Pi3B but I wanted to make use of the 20MHz option… and the Pi3B was dying with my traffic levels (pre-COVID). Also this was before the optimization of the decoder that now allows specifying the level of effort (-E).
To me it was either buying a Pi4 or… repurposing one of my old laptops for Linux. That route was more fun to do for me, so that’s what I have running now.
As for the Mini versus R2… It was an impulse buy, mostly to see if I can run it at 24MHz with the laptop. Marginal benefits (if any), but this is a hobby for me, so… that’s that!
I’ve been running both the mini and the R2. The R2 can use a higher sample rate than the mini, but the difference is small and not worth the added cost (in my opinon) for the R2.
You can use the mini (or R2) to feed most (if not all) sites since the software used for decoding the messages supports the most common formats that are used.
Check out the scripts by @wiedehopf at his Github pages for more info.
I don’t have a lot of time to reply to things at the moment but yes, the highest I’ve ever seen (and been able to screenshot) was 592 when we had that huge opening in late December 2019.
I’d be happy to do a side by side test if someone wants to send me an €800 Radarcape to play with.
I’ve looked at the radarcape demo site in the past and seen higher frame rates than I’ve seen on my airspy ~3500/s, but I don’t know if the number is directly comparable.
Looking at the stats page for the UK, of the top 100 receivers there are 3 which are listed as having an FPGA based reciever - 1 Airsquitter and 2 Radarcapes, in positions 20, 64 and 82 (maybe a few more feeding via piaware, but it’s impossible to see those). Two of those are adjacent to London and one pretty close to EGLC which is also quite close to me and should see roughly similar traffic. I think at least 5 of the top 10 UK stations are using airspys. It may not be significant given the reduced traffic at the moment, but maybe it says something.
Anyway I’m pretty happy that I could rebuild my entire receiver setup from scratch for less than it would cost for one of those hardware based receivers alone.
One further question…can the Airspy Mini bias-t be used to power the RTL Triple filtered 1090 LNA? I understand it’s ok with the Uputronics filtered LNA but I’d prefer to use the RTL one
Yes it can, and I have done it but strictly speaking the rtl-sdr.com lna exceeds the specified 50mA limit. Whether it is safe to do it long term I don’t know. I use an external bias-t which is powered from the pi GPIO pins.
Thanks for the reply. I’m not very technical and wouldn’t know where to start with an external bias-t so I’ll stick with the Uputronics LNA for now until I can get my head around bias-t.
Do I need to disable this bias-t software when I use the Airspy Mini, or will it not affect the Airspy? If i need to disable, how would I go about that?
I am operating an AirSquitter which was replacing my Raspberry PI4 with the blue FA stick.
While the amount of Aircraft was the same, the message rate went up by approx 20%.
As I got it during Pandemic times, the full power is not shown so far. What i clearly can see is a higher number of messages/aircraft.
During peak days, it went up to 1400 messages for 100 aircraft (approx 80 ADS-B). That’s a value i never reached with the FA stick, even not with the peak of 160 aircraft at a time.
So showing full power requires a higher amount of traffic.
I had a short discussion with wiedehopf about it and he said he did not expect a higher performance by using an Airspy based on my traffic and location.
If I read their website correctly, you can’t get access to data you receive externally and have to use the built in feeders unless you pay €500 on top of the €300 device cost for a commercial licence. That is not a good value proposition considering I could likely buy everything I need to replicate my current receiver for under £200, which would have no restrictions on what I do with it. I doubt very much it provides £500 worth of extra performance.
