[Discuss-gnuradio] usrp2_fft.py hehaves abnormally at a certain decimati
[Discuss-gnuradio] usrp2_fft.py hehaves abnormally at a certain decimation rate
Tue, 8 Sep 2009 09:59:03 +0900
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.
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