[USRP-users] FM Transmitter works well, Underruns after adding constant multiply block

salingle salingle at yahoo.com
Fri Feb 24 08:56:34 EST 2012

Dear Knowledgeable People,

Just starting out with an E100 and UHD, have a basic FM transmitter that works nicely (transmitting a wav file, listening on dinosaur FM radio). 

This works nicely:

Wavfile source (32ksps) -> blks2_wfm_tx(320ksps)->uhd_usrp_sink (interpolation of 400)

However, adding a simple multiply by constant block results in repeated underruns:
Wavfile source (32ksps) -> multiply_const->blks2_wfm_tx(320ksps)->uhd_usrp_sink

All of the above is done with python.  Is it as simple as the multiply block takes too long?  Would the same path work if coded in C?  Or, is some other principal being violated?

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