Can't drop sample rate below ~2.1MSPS

Question

I'm running against a processing speed issue with the PicoZed SDR that would likely work better with a lower sampling rate. I'm unable to set the sample rate below about 2.1 MSPS right now, though. The actual minimum seems to be somewhere between 2.083 and 2.084 MSPS. The examples in the GRC files that come with the Analog SD card start at ~1.5 MSPS, which doesn't work at all. Do I need to set another clock somewhere to get lower sample rates? If so, how do I do that?

Thanks in advance.

andrew_senior · Accepted Answer

Not sure if you're still looking for an answer to this 5 months on, but just in case, the reason you can't go below 2.084 Msps is two fold:

1. The minimum ADC rate is 25 MHz, according to this post from ADI: https://ez.analog.com/docs/DOC-12763 (This restriction is enforced by the Linux driver)

2. To get decimation/interpolation factors greater than 12 in the Rx/Tx chains, you need to enable the Rx/Tx FIRs and use decimation/interpolation of 2 or 4.

So, if you use the Rx FIR with a decimation of 4, you can get a sample rate of 25 MHz/48 = 520.833 kHz.

Of course the FIR must be loaded with appropriate filter coefficients when it is enabled.

Can't drop sample rate below ~2.1MSPS

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