Interesting Discussion on Changing Parameters at Runtime

Reference : http://gnuradio.4.n7.nabble.com/how-to-achieve-change-values-of-parameters-at-runtime-tt29993.html#a29995

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tx.ofdm_tx._tx_freq is just a variable holding the frequency, but does
not set it.

You have to re-tune the usrp (tb.set_freq(new_freq)).

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