Forum: GNU Radio GNURadio Run with USRP2 Hangs on Execution

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98cda97ac889e9a4f20309c4f39125fa?d=identicon&s=25 Paul B. Huter (Guest)
on 2013-10-24 00:40
(Received via mailing list)
I finally got my GNURadio Python script running, but after I execute the
script, I get a UHD Warning about requested decimation (a few lines of
text), then a single 0 on a newline, and nothing. I let it run for about
five minutes, and my output file didn't change from 0 bytes.

I am trying to capture the entire shortwave frequency spectrum to
later (hence the output file). I am using a sample I found online,
for GNURadio 3.7. I have set the following parameters

samp_rate = 30000000 (for 30MHz)
tune_request = 15000000 (for the middle frequency)
self._head = blocks.head(8, int(1000000)) (that is what the example
to use for number of samples, but I will likely change that once I
everything is working correctly)

I am not getting any errors, like I was initially before converting it
to 3.7, except not doing anything for five minutes and the output file
not growing.

Links to similar projects are welcome, and any feedback/help is
Bc7e5a4798b9bb4e311a26b41dce2fbc?d=identicon&s=25 Ian Buckley (Guest)
on 2013-10-24 01:36
(Received via mailing list)
With (the default) 16bit complex sample format the maximum sample rate
supported on USRP2 is 25Msps, simply because that is pretty much as much
data as you can get over 1G Ethernet in one direction.
50Msps is supported if you use 8bit complex samples and loose some
dynamic range.

The decimation rate must be an integer, thus 25Msps is a decimation rate
of 4 from the raw ADC converter clock of 100MHz. Also, since the receive
DSP chain cascades 2 Halfband FIR filters (each with fixed decimation of
2) before a CIC filter (With arbitrary integer decimation), it is
preferable to always use decimation rates that factor by 4 so that both
half band filters are active which results in the flattest passband. UHD
will automatically use the half band filters in preference to the CIC
when possible with the specified decimation.

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