Pretty sure it will still depend on the individual location if 20 MHz and the 3B+ will work together.
It needs a really solid power supply. (and a fan or at least heatsinks don’t hurt either)
But better chances now 
Most of the CPU usage still lies in the preamble detection, but if any optimization can help with threshold hardware, it is most welcome. Let’s see how this turns out.
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I’m Ok for trying, but where download this new version ?
Ok i find the download link, and i have tested with a Pi4 and an Airspy mini at 24Mhz, and this is the result :
airspy_set_samplerate() failed: AIRSPY_ERROR_LIBUSB (-1000)
Maybe I did not do things right ?
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24MHz is only supported by the R2.
Oops I misunderstood !
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A higher core frequency can be added to the firmware, but then you need to run it with a cryogenic cooler.
Would it be sufficent with a peltier cooler? Strapping the peltier cooler to the airspy mini case? Or does the cooling need to be directly on the pcb/curcuits?
This discussion about the updated airspy should be moved in the dedicated airspy thread…
I have flagged the first post as “off-topic”, hopefully a mod will do the Herculean work of moving all the following posts.
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With 20MHz, at around 800 messages/sec, Pi3 B drops out of MLAT.
I swapped back to the Pi3+ I used before.
There were a few lost samples directly at the start, but not after that. Aircraft count is around 120 a/c and messages at 1400msg/s.
The Pi3+ worked ok before, though with only a few lost samples here and there. Do not remember CPU usage or anything, unfortunately.
I just pushed a new version with more preamble optimizations. The CPU usage reduction is quite significant over the previous build.
Sorry for hijacking this thread. Maybe a new one should be created for testing decoders.
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I’ll just create it
“Airspy ADS-B decoder” seems like a good title.
I have two R2’s running with Odroid’s XU4 and N2, and a number of 3+'s but no 4’s, if I can be of any assistance.
Right, while I’m away on holiday I’ve had two parcels delivered at home which I think are the coax and the new aerial. If that’s the case then it shouldn’t be long before I’m able to get the aerial back up again, except this time it’ll be even higher, I think I worked out that it’ll be 11ft higher than it is now
The level of altitude seem to be more important than many think
I am using my antenna still indoor, but moved it approx 3 feet higher.
Now the range went up from 125NM to almost 150NM in average without changing anything else.
The only problem is now discussions with my wife because i used the broomstick for it
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+1 … I was surprised to see 250nm range from a DIY antenna once I got my ADS-B box 40 feet up with no nearby obstructions. I assumed i would need a FA antenna and possibly a LNA to get that range.
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Sorry for the late reply.
Thanks for the info, very usefull!
I read somewhere the Airspy has much better strong signal handling than other dongles, which in my case (close to an airport approach) would be preferable. Also near GSM tower plus strong FM broadcasting, so conditions are tricky.
Both common filtered LNAs will handle those conditions fine in combination with an rtl-sdr compatible dongle.
And if you buy an Airspy, you’ll want to buy an LNA as well for best reception.
The Airspy isn’t as sensitive as for example the ProStick+ with builtin amplifier, so you need an external LNA (filtered LNA much preferred for ADS-B).
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I lowered my receiver when I put the new hexbeam on but last weekend, I fitted a new aerial to the top of the hexbeam and replaced the Pi3B+ with a Pi4B.
You can see the aerial in the blue box here and the new location of the receiver itself in the red box. I’ve dropped the receiver just a few feet as it was slightly easier to manage the cables. Of course, that doesn’t really matter any more, it’s the position of the aerial that’s important.
The new aerial is now 11ft higher than it used to be, taking it up to 44ft (13.5m) AGL.
I’m still tweaking the Airspy settings but this full day heatmap from yesterday demonstrates what a clear view it has now.
I really can’t see how I can make any other improvements to this setup now, certainly not regards to aerial location. I suppose I could replace the Airspy Mini with an R2 but then it’s really getting into diminishing returns and that just isn’t worth it.