[USRP-users] Switching and high spike in spectrum

bob wole bnwole at gmail.com
Wed Oct 29 13:54:52 EDT 2014

USRPN210r4 with SBX

I am observing a strong spike at the center of the receive spectrum when I
start burst transmission.

My top flowgraph contains following two hierarchical blocks
 1) A transmitter flow graph with (tx_time, tx_sob, tx_eob)
 2) A receiver flow graph

When I run top flowgrpah (without transmitting anything) and observe the
FFT of the received signal the spectrum does not contain high spike in the

But as soon as I start transmitting in burst mode I see a very high spike
in center of the received signal FFT spectrum. It looks like LO
(transmitter or receiver ) is being received? Which one is it ? And why is
it happening?  How can I avoid it because it is affecting my packets.

When I apply the offset in digital using DDC/DUC, the spike moves out of
the band.

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