Transceiving a sinusoid using usrp's

Hi,

I am trying to send, then receive and finally display a sinusoid of
arbitrary frequency say 128KHz using two usrp’s and two computers. I
have used grc on both computers to do so.

On tx computer, the flow graph of grc is:

signal source --> usrp sink

In signal source, I set the frequency of cosine wave=128K,
amplitude=10K, offset=0, output type=complex, sample rate=256K. In usrp
sink, I set input type=complex, interpolation=128M/256K=500,
frequency=900M, gain=0dB, side=A, transmit=enable (I am using flex900
daughter boards)

On rx computer, the flow graph of grc is:

usrp source --> scope sink

In usrp source, I use output type=complex, format=16 bits,
decimation=64M/256K=250, frequency=900M, gain=0dB, side=A, RX
antenna=TX/RX, half band filters=enable. In scope sink, I simply choose
the type=complex, sample rate=256K, then all other parameters are
default.

When I run all this, a wave form like tone modulation (amplitude
modulation of a sinusoid with another sinusoid) is displayed on the
scope while I get something displayed on the terminal as:


TX:
A: Flex 900 Tx MIMO B
r.baseband_frequency = 904000000.0
r.dxc_frequency = -4000000.0
r.residual_frequency = 0.0
r.inverted = False
RX:
A: Flex 900 Rx MIMO B
r.baseband_frequency = 896000000.0
r.dxc_frequency = -4000000.0
r.residual_frequency = 0.0
r.inverted = False


And when I stop the simulation on tx computer, a sinusoid waveform of
frequency about 4.4 KHz is displayed on rx computer. Can anyone please
suggest something in this regard?

Thanks,
Mahboob

On 12 July 2010 15:52, Rahman, Muhammad Mahboob Ur
[email protected] wrote:


And when I stop the simulation on tx computer, a sinusoid waveform of frequency about 4.4 KHz is displayed on rx computer. Can anyone please suggest something in this regard?

Maybe you see the carrier because the transmitter is not shut down
when you stop the flowgraph. This happens if you have the Transmit
parameter of the USRP sink set to “Enable”. If you use “Auto T/R” the
transmitter will stop when the program stops.

Alex

Alex,

You are right. “Auto T/R” is the right option to use. One little thing,
the usrp source/sink block takes a parameter “gain(db)”, what is the
maximum value that I can specify here? Is it 32db? Also, what maximum
amplitude value I can specify in signal source block? Is it 32767?

Thanks.


From: Alexandru C. [[email protected]]
Sent: 12 July 2010 11:13
To: Rahman, Muhammad Mahboob Ur
Cc: discuss-gnuradio
Subject: Re: [Discuss-gnuradio] transceiving a sinusoid using usrp’s

On 12 July 2010 15:52, Rahman, Muhammad Mahboob Ur
[email protected] wrote:


And when I stop the simulation on tx computer, a sinusoid waveform of frequency about 4.4 KHz is displayed on rx computer. Can anyone please suggest something in this regard?

Maybe you see the carrier because the transmitter is not shut down
when you stop the flowgraph. This happens if you have the Transmit
parameter of the USRP sink set to “Enable”. If you use “Auto T/R” the
transmitter will stop when the program stops.

Alex

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