CODEWITHSUNDEEP
gnuradiousrp
Esperius
Esperius

Reputation: 11

Usrp1 and Gnuradio

I am trying to set up 5 USRP1 and some daughterboards on 2.4 and 5 GHz.

Some of them are out of order and some work properly, but I don't know which is which. I am trying to send a symbol (QAM modulation) sequence then I am trying to pass it with a file source to both a USRP sink and an FFT sink.

I am trying to find articles and tutorials, how sample rates are connected and how to set up them but I can't understand what am I missing. Could somebody please help with the schemes?

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Upvotes: 1

Views: 447

Answers (1)

Marcus Müller
Marcus Müller

Reputation: 36352

128 MS/s is not a rate that is possible with the USRP1. The console will contain a UHD warning that a differen, possible rate was chosen (most likely, 8MS/s).

Now, you contradict that rate by having a "Throttle" block in your flow graph - that block's job is only (and nothing more) to slow down the average rate at which samples are being let through – and that is something your "USRP Sink" already does. In fact, modern versions of GRC will warn you that using a throttle block in the same flow graph as a hardware sink or source is a bad idea.

Now, you'll say "ok, if the USRP sink actually needs to consume but 8MS/s, and my interpolator makes 128 MS/s out of my nominally 1M/s flow (really, signals within GNU Radio don't have a sampling rate), then that's gotta be fast enough to satisfy the 8MS/s demand!".

But the fact is that a 128-interpolator is really a CPU-intense thing, and the resulting rate might not be that high, made even worse by the choppy nature of how Throttle works.

In fact, your interpolator is totally unnecessary. The USRP internally has proper interpolators for integer fractions of its master clock rate 64MS/s, which means that you can set the USRP Sink to a sampling rate of 1MS/s and just directly connect the file source to it.

Upvotes: 1

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