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From: | Marcus D. Leech |
Subject: | Re: [Discuss-gnuradio] UHD Warning on ODD Interpolation |
Date: | Thu, 01 Aug 2013 08:28:02 -0400 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.24) Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16 |
On 08/01/2013 08:16 AM, embyte wrote:
Hello list,I have a graph consisting of a modulator mixed with a signal source, and a USRP sink.I have it configured with a *sampling rate* of 720KHz.When I run it, UHD fires the following warning (and transmission seems fine).The requested interpolation is odd; the user should expect CIC rolloff. Select an even interpolation to ensure that a halfband filter is enabled. interpolation = dsp_rate/samp_rate -> 89 = (64.000000 MHz)/(0.719101 MHz)What is this about? Thanks. _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Two problems:(1) 720Khz is not an exact integer fraction of 64MHz (the sampling rate of the device)--so it rounded
(2) It's warning you that you'll get a "humped" frequency response with more rolloff than you'd like, due to the rounded-down sample rate
requiring an interpolation rate that is not divisible by two. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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