Frequency Translating FIR Filter

I am trying to view the spectrum from 0-1MHz recorded at 50M. I used a
low
pass filter to only record 0-30MHz. My frequency translating filter is
defined as follows:

Decimation: 50
Taps: firdes.low_pass(1, samp_rate, 500000, 100)
Center Frequency: -500000
Sample Rate: samp_rate

samp_rate: 50M

Any ideas?

Paul B. Huter

Forgot to mention I am running the filter output to an FFT Sink.

Paul B. Huter

On Fri, Nov 22, 2013 at 7:14 PM, Paul B. Huter [email protected]
wrote:

Any ideas?

Paul B. Huter

Let’s take a look at what the frequency_xlating filter does:
http://gnuradio.org/doc/doxygen/classgr_1_1filter_1_1freq__xlating__fir__filter__ccc.html

It filters a signal at the center frequency you set and then moves
that signal to baseband. You’ve set a sampling rate of 50 Msps and a
center frequency of -50 kHz. Which means you want to get the signal at
-50 kHz moved to baseband. The output signal will be from -500 kHz to
+500 kHz.

You should basically be seeing what you would if you set the center
frequency to 0 since you’re only moving 50 kHz out of 1 MHz of
spectrum.

What’s the exact problem you’re facing, then?

(Also, once again, you’re setting a very tight transition band here
that would cause a gigantic filter.)

Tom

I changed the transition band to match the 5M transition band I used on
the
low pass filter to record the data and things worked.

Paul B. Huter

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