I was in a test with 'usrp2_fft.py' code in the gr-utils directory and found
that the program is not running as I expected in certain conditions.
I was watching signals running the usrp2 as a spectrum analyzer with the
code.
Test environment information
- usrp2 + gnuradio 3.2.1 (or gnuradio 3.2.2)
- usrp2 H/W version : rev. 3
- usrp2 SD card image/code version : Cannot identify
- RF RX Interface : basic RX board
- Host PC O/S : ubuntu 9.04 Desktop (64bit version)
Symptom
- When I set the decimation rate to '20', and open the RF input
port(hooked up no signals), the noise level goes down to -380dBm and and
flat. With the decimation rate of 18 or 22, it looks O.K. Noise level is
around -90dBm and I can see the frequency domain envelope of white noise.
- At that moment, the samples coming from usrp2 are all zero. I
confirmed it with wireshark.
- I figured out that it happens not only with the decimation rate of 20,
but with 40, 60, etc.
I was suspicous if it went like that with multiples of 20, but it
happened with 50, 82, etc.
- When I feed signal to the RF RX port, it goes back to normal. So, I
can say that it happens when the input signal level(power) is lower that a
certain level. However, it does not happen with other decimation rates like
4, 6, or 18.
I would like to know
1. If this is a known issue. In that case, I also would like to know if
there is any workaround.
2. If this is a new issue, I would like to ask experts in this mailing list
to reproduce the experiment and let me know why this happens and what I
should do.
Best regards,
ILKYOUNG.
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