[USRP-users] missing rx_freq tags when frequency changes

David Rose David.Rose at govsco.com
Tue Nov 7 21:21:07 EST 2017

I'm programming a USRP B200mini-i in Python.

When the receiver starts up, it automatically inserts a 'rx_freq'  tag into the stream.

In my application I periodically change the receiver frequency using a command such as: self.uhd_usrp_source_0.set_center_freq(self.rf_freq, 0).  This does indeed change the frequency, but it doesn't look like the source block is adding new 'rf_freq' tags to mark the changes.  Does anyone know how to make that happen?

I tried directly setting a class variable in a downstream block from top_block every time I change the frequency.  That sort of works, but I don't think it's marking the exact right place in the stream, so I assume that's not a recommended approach.

Finally, does the B200mini-i require any settling time after a frequency change, and if so, how much time?  Is there a chance of getting bad samples during a frequency transition, or does the stream shut down until things stabilize?


Dave Rose
Valkyrie Systems Corp.

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