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…..you 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.
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