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Re: [Discuss-gnuradio] Transmit filtering

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Transmit filtering
Date: Mon, 5 Sep 2011 12:59:11 -0400

On Mon, Sep 5, 2011 at 12:55 PM, John Ackermann N8UR <address@hidden> wrote:
Hi Marcus --

I am selecting complex taps from the drop down, but still get an error at runtime if either cutoff frequency is 0 or smaller.




That sounds like a bug in the GRC block, then. I just tried this as a complex BPF and it works fine:

gr.firdes.complex_band_pass(1, 1, -0.1, 0.2, 0.1)

However, as was already mentioned, if you are trying to create a bandpass filter from -40 to +40 kHz, that's just a low pass filter with a bandwidth of 40 kHz:

gr.firdes.low_pass(1, 100e3, 40e3, 2e3)

Will give you a filter for this purpose. Substitute your own sampling rate and transition width, of course.


On Sep 5, 2011, at 11:46 AM, "Marcus D. Leech" <address@hidden> wrote:

> On 05/09/11 10:19 AM, John Ackermann N8UR wrote:
>> I'm generating two NBFM signals, offsetting them plus and minus 25 kHz
>> with FreqXlatingFilters, and combining the output in an adder which
>> then drives a USRP sink.  It seems sensible to put a bandpass filter
>> on the result.
>> I have a basic conceptual confusion.  I would think that you'd specify
>> a bandpass filter around zero with a low cutoff of, say, -40e3 and a
>> high cutoff of +40e3.  However, this doesn't work -- the bandpass
>> filter seems to require a number >0 for the lowpass frequency.
> Make sure that you specify complex-taps.  I assume you're using GRC.  By
> default, it uses the version of
>  the bandpass filter with real taps.  But if you specify complex taps,
> you can use negative frequencies.
> --
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
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> Discuss-gnuradio mailing list
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