SDRplay API Updated

The SDRplay API has recently been updated to version 1.94. They have also released version 3.9 of their EXTIO plugin. The changes include

  • 10kHz lower limit frequency support
  • 10MHz sample rate
  • Decimation of the sample rate for improved noise performance
  • Improved performance
  • Better function support for developers
  • Callbacks used for stream data and gain updates
  • Tuner AGC function moved to the API

The major changes for users appears to be the the 10 MHz sampling rate and the addition of decimation. The 10 MHz sample rate increases the visible spectrum, however it appears that the maximum IF Bandwidth is still only 8 MHz, meaning that the outer edges of the spectrum won’t show any signals. However,. but the IF filter roll off is not super sharp, meaning that the full 10 MHz should still be usable, with only minor attenuation at the edges. However, we note that in our testing we noticed some roll off at the edges, giving us about 9 MHz of usable spectrum. There should also be an improvement in SNR by using the higher sampling rate thanks to decimation.

Edit: Jon Hudson from SDRplay wrote in to let us know that our assumption of the outer edges being useless was incorrect (the crossed out text). He writes:

I noted one error in what you wrote there… suggest that the 10 MHz of visible B-W is worthless because the IF bandwidth is only 8 MHz max and hence you can’t see any signals beyond that 8 MHz window. This isn’t true. The IF filters start to roll off at 8 MHz, but they are not brick wall filters. The actual roll off is at +/- 5 MHz (10 MHz of bandwidth) so within that 10 MHz, at the edges, there are only a few dB of attenuation, and because the CNR has been defined by the front end circuits ahead of the IF filter, any filter attenuation will be applied equally to the signal and the noise leaving the Carrier to Noise ratio unaffected. As a consequence, whilst the user may seem some roll off, the ability to see and receive signals that may lie at the outer edges of the 10 MHz bandwidth is unaffected.

In this update they also added visual decimation controls. This is useful as this allows you to zoom into a signal without loosing resolution whilst maintaining a high sample rate. The decimation controls only appear to activate in the lower IF Bandwidth settings.

The SDRplay RSP is a $149 USD software defined radio with 10 kHz to 2 GHz tuning range, 12 bit ADC and up to 8 MHz of visible bandwidth.

The new RSP EXTIO control panel showing decimation and 10 MHz sample rate.
The new RSP EXTIO control panel showing decimation and 10 MHz sample rate.
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DoaJC Blogger

Does decimation refer to that effect in which a signal stands out better in the waterfall the higher the samplerate is? I noticed and wrote of this effect on ATSC signals and how they look “contrastier” and seem to have greater signal strength when I select 8 instead of 7 MHz.

Also, if Jon Hudson’s statement about the outer edges is true, we should be able to receive LTE. The possibility is very exciting but sounds dubious because the IF filter’s 6 MHz roll-off is too great to permit ATSC decoding, which suggests to me that a signal cannot be decoded unless your IF filter exceeds the signal’s bandwidth by a small margin. Still, the SDRplay team keeps surprising me so maybe they’ve worked out a solution.


@Truth “Imitation is the sincerest form of flattery” Indeed it is.

Decimation and oversampling to increase dynamic range/SNR have been known since the early 1960s. First large scale commerical application of oversampling started in the mid 1980s.

The real innovation, IMHO, for the AirSpy, SDRPlay RSP, and RTL-SDR dongles is price. That makes them fun to play with and experiment with. If I destroy one by doing something stupid, I go out and buy another one. Not a big deal.

If on the other hand, if I destroy a $120K real-time spectrum analyzer by doing something stupid, that WILL hurt and I will be looking for employment opportunities elsewhere.

Product selection, IMHO, really comes down to requirements and support.


Well… where can i get it? The downloadable version on their website doesnt seem to be the new version
In SDR#, Recording with a SDRPlay won’t work, Noise reduction/IF&AF Noise reduction wont work… What kind of fuckery is going on here? Cucking all other SDRs but their own one? dropped

jintau jt

Nobody complains when high price of sdr sw lacks full support for a competing product …. why is the different opinion with these low-end products of the price? the sdruno sw is compatible with airspie and no full support for rtlsdr. I really like sdrsharp but he should not be making money for their products direct competition. it is known sdrsharp is not supporting sdrplay to the full.


“Imitation is the sincerest form of flattery.”

Isn’t that how AirSpy works since 3 years ago? They will eventually ditch their own tuner and use the R820T2 at some point.