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Re: [Discuss-gnuradio] GNURadio Run with USRP2 Hangs on Execution

From: Paul B. Huter
Subject: Re: [Discuss-gnuradio] GNURadio Run with USRP2 Hangs on Execution
Date: Wed, 23 Oct 2013 16:44:37 -0700


Thank you for your detailed response. If I stick with eight bits and
increase to 50Msps, will that solve the decimation rate problem? I
realize this would result in a decimation rate of two, which would not
be ideal. I may decide to only grab 25MHz, not the full 30, to keep
the decimation rate at four.

Thank you, again.

Paul B. Huter

Ian Buckley <address@hidden> wrote:

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


On Oct 23, 2013, at 3:39 PM, Paul B. Huter <address@hidden> wrote:

> 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 analyze 
> later (hence the output file). I am using a sample I found online, modified 
> 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 stated to 
> use for number of samples, but I will likely change that once I verify 
> everything is working correctly)
> I am not getting any errors, like I was initially before converting it all to 
> 3.7, except not doing anything for five minutes and the output file size not 
> growing.
> Links to similar projects are welcome, and any feedback/help is appreciated.
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