Error in testing benchmark_tx/rx.py

I’m currently testing UHD.
I use two USRPs with one SBX on each.
and I got GNU Radio 3.5.0rc0 on Ubuntu 10.10 and benchmark programs
supporting UHD.

When I run benchmark_tx/rx.py, however,

[email protected] $ ./benchmark_tx.py -f 410M
[email protected] $ ./benchmark_rx.py -f 410M

I can see ‘dots’ representing a signal is transmitted on a transmitter
side.
but a receiver does give nothing on a screen.

and the screens on the both side, I got this message.

No gain specified.
Setting gain to 5.750000 (from [-20.000000, 31.500000])

UHD Warning:
The hardware does not support the requested TX/RX sample rate:
Target sample rate: 0.050000 MSps
Actual sample rate: 0.250000 MSps

Symbol Rate: 25000.000000
Requested sps: 2.000000
Given sample rate: 250000.000000
Actual sps for rate: 10.000000

Requested sample rate: 50000.000000
Actual sample rate: 250000.000000

What did I do wrong?

  1. Wrong frequency option (either tx or rx)
  2. Wrong/Unspecified sample rate option (either tx or rx)
  3. Too weak signal strength to catch
  4. Or…?


Seokseong Jeon,PhD Candidate
Communication & Networks Lab
IT Convergence Engineering (ITCE), POSTECH, Korea
+82 10 8338 1229,gee.songsong at gmail . com


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On Sun, Nov 20, 2011 at 1:57 AM, Songsong G.
[email protected]wrote:

Thank you for all of you.

I’ve got some progress on it.

From Tom’s suggestion I give options to benchmark_tx.py
$ ./benchmark_tx.py -f 450e6 --tx-amplitude=0.02 --tx-gain 30 -S 10

And looking its spectrum,

I could get a distinct frequency component around 450 MHz.

After that, I ran benchmark_rx.py
$ benchmark_rx.py -f 450e6 --rx-gain=50 -S 10
(I modified receive_path.py to have threshold with -80 dB to filter out
others)

And I got a following result.

This means that I did wrong in either trasmitting or receiving.

  1. Still signal is clipped (but, I guess not, --tx-amplitude=0.02)
  2. Threshold value is mistaken (threshold = -80 [dB])
  3. sample per symbol (-S 10)
  4. –tx-gain, --rx-gain might be wrong.
  5. or something I am missing.

Please give your suggestions. I am almost close to the goal.
And thank you for all of you in advance

Yes, you are close. It’s probably a matter of tweaking the receiver gain
and the transmit power to the right levels. We have a digital AGC, but
that
doesn’t do much for the important analog gain stages you need to get the
signal right.

It could also be a frequency offset, although your graph showed that the
signal looks pretty well centered. It be good to zoom in, though, or use
the uhd_siggen to transmit just a tone and find out how far off
frequency
you are.

Tom

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