Hi,
Would you plz tell me the best way to set the gain values for Rx/Tx
USRP with benchmark_tx and benchmark_rx at command line. How to
adjust these values?
Thanks.
On 03/14/2013 07:41 AM, Nada ABDELKADER wrote:
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The process is trial-and-error and involves a lot of things, including
but not limited to:
- free space loss between the transmitter and receiver
- whether the transmitter and receiver are so close that you’re
coupling signals on the front-end unintentionally - noise
My recommendations:
- Open up an FFT plot using uhd_fft on the receiver and set the gain
slider somewhere in the middle (tune it to Rx freq, obviously) - Run benchmark_tx.py on the transmitter with default gain and
tx-amplitude settings - See how strong the signal looks on uhd_fft. I’ve found you need 25 or
30+ dB SNR to make it work (I don’t remember the exact numbers) - If you have a board with no front-end gain, such as RFX2400, increase
the tx-amplitude parameter in small steps and see if you get better
results. If you see clipping/compression - you’ll see a big, wide, ugly
signal on uhd_fft - you’ve gone too far. Keep in mind that the gain is
specified in the range [0, 1.0] inclusive, but the lower and upper
regions don’t produce a clean, linear signal. You should stay in the
0.1-0.2 range but your mileage may vary. - If your board does have front-end gain, leave the tx-amplitude at its
default value and change the gain only. - You may have to adjust the uhd_fft Rx gain, but again, beware of
clipping on the Rx side. - Once you think you have the numbers right, try running benchmark_rx.py
with the same Rx gain setting you found with uhd_fft.py and the same Tx
gain settings you found for benchmark_tx.py.
HTH.
–sean