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Re: [Discuss-gnuradio] Low-pass filter


From: Paul B. Huter
Subject: Re: [Discuss-gnuradio] Low-pass filter
Date: Mon, 18 Nov 2013 09:56:49 -0600

Thanks, Tom. I do intend to decimate the 50MHz input by 50 to have 1MHz. Is that correct?

Also, if I take my 50MHz source USRP, and run it through the filter with decimation and low pass filter set to 15000000 (15MHz)
center frequency @ 15000000 (again, 15MHz)
Taps = firdes.low_pass(1, samp_rate, 15000000, 100)

Will that give me a 30MHz signal to save to a data file and run back through the filter I initially asked about?

Thanks.

Paul B. Huter

On Nov 18, 2013 9:46 AM, "Tom Rondeau" <address@hidden> wrote:
On Mon, Nov 18, 2013 at 10:35 AM, Paul B. Huter <address@hidden> wrote:
> If I want to use a low-pass filter to look at 1MHz blocks of data, is it
> appropriate to use the following parameters:
>
> low pass filter: 500khz
> center frequency: -500khz (for 1MHz, increments of 1MHz for others)
> Taps: firdes.low_pass(1, samp_rate, 500000, 100)
>
> Paul B. Huter

For a low pass filter, you specify the passband bandwidth, but it's a
real-valued filter, so it's symmetric about 0. So, yes, if you set the
bandwidth of the filter to 500 kHz, then the filter will filter from
-500 to +500 kHz.

If you just want to look at 1 MHz of spectrum, I suggest you also
decimate the incoming signal so that you reduce your processing
requirements as well as filter.

Tom

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