[Discuss-gnuradio] Simultaneous transmit and multichannel receive on USRP1

[Young Lee]

Hello everyone,

I was wondering if someone could either point me to an example or give
me some tips on how I can get setup gnuradio to do simultaneous
transmit and receive on multiple channels. At the moment, I just need
to transmit on one channel but need to receive on 4 independent
channels.

I am running gnuradio 3.2.2 on Ubuntu 9.04. I have a USRP-1 with 2
LFRX boards and 1 LFTX board.

Following the USRP code examples that came with gnuradio, what I've
been able to do successfully so far is:
--simultaneously transmit and receive on single channels.
--receive on 4 independent channels.

If I then take my working multi-channel receiver and just add a line
to create a transmitter sink object with usrp.sink_c(), all 4 receive
channels show sequences of alternating 0, -1 values instead of the
digitization of the signal that I'm putting into the input channels. I
don't have this problem if I modify my receiver to receive on just one
channel -- I can then transmit and receive simultaneously without
problems.

Any ideas on what I'm doing wrong here?

thanks
Young