Re: Rafael Micro R820T2 now discontinued #airspy


I believe the gain distribution control predated AirSpy usage. That came pretty early on. The first rtlsdr.dll drivers I encountered used the compromise concept for setting all the gains in the E4000 and the three gain settings in the R820. I think, but I'd not sure, that someone went in and broke out the three R820 gain controls as much as a year before AirSpy. But it was not generally adopted.

Another feature not generally adopted when AirSpy came around is slightly more accurate tuning mechanisms. The early rtlsdr.dll R820 implementations had some bad arithmetic which led to some "inaccurate" results. (Who notices 10s of Hz when the dongles are 10s of kHz off frequency?) Then a test implementation came around that provided something like 7 Hz accurate resolution for frequency settings within the dongle using cleaner math and fine tuning with the Realtek A/D converter/USB chip.

Bandwidth control is something AirSpy introduced. This was the really serious AirSpy innovation. It was vaguely known about judging from the rtlsdr.dll code. But it was hard coded with apparently "TV" sorts of settings and left that way.

The someone's involved include but are not limited to:
Steve Markgraf <>
Dimitri Stolnikov <>
Hoernchen <>
Kyle Keen <>
Oliver Jowette <>
Leif Asbrink <>

I collected a lot of the work and added a little of my own to the version I posted to GitHub. (Thanks are due for all of them for their work.)


On 20180308 04:34, prog wrote:
On Thu, Mar 8, 2018 at 03:38 am, Priyasloka Arya wrote:
Thanks for the update Youssef. Did you have any chance to evaluate or gather
first-hand information about the performance of R820T2 siblings( (R828D2,
R836, R840 )mentioned by you?
The newer tuners are slightly better (lower NF, more DR), but are also more complex and require a lot of work to get right. The datasheets I got in hand reflect different generations with different architectures, but getting a few protos of each tuner can go very quickly.
The driver we wrote for the R820T is slightly different from the original RTL-SDR version (which was written by non-RF linux kernel developers). Things like the tunable IF filter, and fine gain distribution control etc. were first introduced in Airspy because we needed them, then they were backported to many RTL-SDR forks. I expect someone has to do the same job again for the newer tuners.

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