Re: [Discuss-gnuradio] On Off Keying

[Johnathan Corgan]

On Mon, Sep 29, 2008 at 2:28 PM, Brian Padalino <address@hidden> wrote:

> Don't some of the daughterboards also have some AGC built in?  I can
> see if the interpolation rate is not high enough, the signal power
> will not go down enough (especially after the RRC filtering) to really
> look like much of a difference if any due to the AGC circuitry and
> other transients that may occur on signals quickly coming on then off.

None  of the daughterboards have AGC as far as I'm aware (Matt,
correct me if I'm wrong on this.)

It's not that the filtering is preventing the envelope from going to
zero (though it might be; RRC's are intentionally designed to
introduce ISI in a very specific way).  It's just that with the
waveform he's sending, there is a strong carrier component at passband
that shows up as a constant beat frequency in the receiver due to
frequency offset.

> Please correct me if I am wrong, but I think using a very large
> interpolation rate might help clarify the situation.

It would improve things.  If the baseband "square wave" had it's
fundamental frequency near the RRC filter limit, or near the Nyquist
limit of the baseband sampling rate if the RRC wasn't in use, there
would be few to no harmonics that make it through the filtering and/or
interpolation.  The transmitted waveform would be a carrier and two
sidebands, a classic AM waveform. I think that's what he is seeing.

-- 
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com/