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Re: [Discuss-gnuradio] TX/RX simultaneously using one USRP board

From: David Scaperoth
Subject: Re: [Discuss-gnuradio] TX/RX simultaneously using one USRP board
Date: Thu, 13 Apr 2006 22:56:23 -0400

No reason... ; ) I just put together two old scripts that I had lying around to see if it would work. My ultimate goal is to receive, demod and change the modulation, and then retransmit, so that's probably what I was thinking about...

hope this clears things up!

David Scaperoth

On Apr 13, 2006, at 10:30 PM, Martin Dvh wrote:

David Scaperoth wrote:
Hey dawei,

I just recently played with the idea of a repeater (receive on
frequency and transmit on another).  ALthough I have personally only
used the TvRx and Basic Tx, the concept is basically the same (I would
imagine) for the FLEX400.  I haven't pushed the data rates, but  for
narrowband FM, it works great. I guessing the only bottleneck might be
the USB (8MSps total), but I like I said, I haven't tested  it.  Here
was my basic flow graph.  It worked like a charm.

dst = usrp.sink_c (0, tx_interp)
self.rx_src = usrp.source_c (0, decim)

self.connect (self.rx_src, rx_amp, fm_demod)
self.connect (fm_demod,rx_filter)
self.connect (rx_filter,tx_filter)

self.connect (tx_filter,freq_mod)
self.connect (freq_mod,tx_amp,dst)
Just curious, why did you first fm_demod and then fm_mod.
You could also do:
if_filter_coeffs = gr.firdes.low_pass (if_gain,                # gain
if_sampling_rate, # sampling rate if_bandwidth, # low pass cutoff freq if_width_of_transission_band, # width of trans. band gr.firdes.WIN_HANN) # filter type

src = usrp.source_c (0, rx_decim)
dst = usrp.sink_c (0, tx_interp)
if_filter=gr_fir_filter_ccf(1, if_filter_coeffs)

self.connect (src, if_filter,dst)


So, essentially the key points are that you can use the usrp as both a sink and source (its duplexing baby!). The underlying code selects the
most likely subdevice (if you don't do that yourself), so its  pretty
easy really. and where I usually have a sink to a file, audio card, or whatever (for a receiver chain), I just simply use that as the source
for my normal transmit.  Here's a link to the source code,  I haven't
spent any time making it look pretty, but it should work. I hope this
helps some!  Good Luck!


David Scaperoth

On Apr 13, 2006, at 1:47 PM, Dawei Shen wrote:

Hi, Eric and other friends

Now I am working on a project that requires simutaneous TX/RX within
one usrp board. I equip too FLEX400 daughter cards on one USRP board.
What I am trying to do is to use the TX to retransmit (i.e. relay)
what the USRP has received from the RX. Is it doable under the current
framework of GNU Radio? If so, could you provide any hints on how to
realize this? An obvious question to me is that in the Python code, we
should either define the usrp as a source or a sink, but in my
application, the USRP board serves as both sink and source. So what
should I do in my case?

Thank you for your input

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