Re: [Discuss-gnuradio] Transmit filtering

[Marcus D. Leech]

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