Simultaneous RX/TX using RFX2400 Boards

Hi,

I have written a code for simultaneous TX/RX for RFX2400 as followed
below:

self.rx = usrp.source_c (0,self.decim)
self.tx = usrp.sink_c (0, self.interp)
.
.
.
fg = my_graph()
.
.
.
fg.subdev.set_enable(True) # Enable transmitter
fg.connect(fg.rx, fg.tx)
.
.
.

When I receive and then transmit, the waveform distortiton is very high
on
transmit path. I used different combination for decimation and
interpolation
rates, but that didn’t work.

I am recieving a sinusoid wave using RX2 port on 2.40GHz and
transmitting
using TX/RX port on 2.48GHz.

Can somebody tell me about the reason for distortion?

Thanks in advance.

Regards,
Tarun
University of Texas -Dallas

On Mar 7, 2007, at 1:47 PM, Tarun T. wrote:

fg = my_graph()
high on transmit path. I used different combination for decimation
and interpolation rates, but that didn’t work.

From your description above, you are transmitting whatever you
receive (is this true?).

I am recieving a sinusoid wave using RX2 port on 2.40GHz and
transmitting using TX/RX port on 2.48GHz.

I’m guessing that the sinusoid is coming from a waveform generator,
or something. Are you selecting the RX2 antenna?
(subdev.select_rx_antenna(“RX2”)) are you using a multiplication
block on the transmitter? What are you setting the Rx PGA gain to?

Can somebody tell me about the reason for distortion?

Thanks in advance.

Regards,
Tarun
University of Texas -Dallas

David

Hi David,
Thank you for you reply.

On 3/7/07, David S. [email protected] wrote:

From your description above, you are transmitting whatever you
receive (is this true?).

Yes, its true and I am interested in transmitting the amplified
signal
which I receive on the RX2 port.

I’m guessing that the sinusoid is coming from a waveform generator,

or something. Are you selecting the RX2 antenna?
(subdev.select_rx_antenna(“RX2”)) are you using a multiplication
block on the transmitter? What are you setting the Rx PGA gain to?

Yes,the sinusoid is coming from a waveform generator and that is using
usrp_siggen.py on another computer/USRP. Yes, I am selecting RX2, and
transmitting on TX/RX without any multiplication block on the
transmitter
end. The RX PGA gain is 75.

Is there any relation with the decimation and interpolation for RX and
TX?

David

Regards,
Tarun

On Mar 9, 2007, at 1:44 AM, Tarun T. wrote:

I’m guessing that the sinusoid is coming from a waveform generator,
or something. Are you selecting the RX2 antenna?
(subdev.select_rx_antenna(“RX2”)) are you using a multiplication
block on the transmitter? What are you setting the Rx PGA gain to?

Yes,the sinusoid is coming from a waveform generator and that is
using usrp_siggen.py on another computer/USRP.

When you send the tone, can you see it on the receiving computer
(with an FFT, or an oscope), and what is the signal level? if its
pretty low (like 10dB or less), you may have to put a multiplication
block in the transmitter.

Yes, I am selecting RX2, and transmitting on TX/RX without any
multiplication block on the transmitter end. The RX PGA gain is 75.

Is there any relation with the decimation and interpolation for RX
and TX?

Are you receiving and transmitting at different sampling rates? I
don’t see why a sinusoid would be distorted because of one sampling
rate over another. What is the frequency of the tone you are
sending? And the sampling rate? If the frequency of the tone is half
(or more of the sampling rate, you may be in trouble).

BTW, What is the distortion you are seeing? are there lots of images
(if there are, you may be transmitting at too high of a signal
level)? is the signal taking up too much bandwidth? FWIW, I have had
experiences where it was less about my USRP, and more about my
settings on my oscope =)

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