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Re: [Discuss-gnuradio] GMSK modulator for higher modulation index


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] GMSK modulator for higher modulation index
Date: Thu, 5 Apr 2012 09:35:37 -0400

On Wed, Apr 4, 2012 at 1:42 PM, wayne roberts <address@hidden> wrote:
> To support GFSK modulations, a higher modulation index needs to be used.
>
> MSK is defined as a fixed modulation index of 0.25.
> However, GFSK is used in many simple ISM (unlicensed) systems, where the
> modulation index can vary from 0.5 to 2.0 typically.    So, I would ask how
> the existing digital FM modulator blocks (such as GMSK mod) could be used in
> such case as (G)FSK.   This is used in low-cost low-power simple systems,
> which are not as spectrally efficient.
>
> I have also noticed in gnuradio-companion, under Digital Modulators:
> "GMSK Mod" which uses file gr-digital/python/gmsk.py, and
> "GMSK Modulator" which uses file gr-digital/lib/digital_gmskmod_bc, which
> just calls digital_cpmmod_bc.cc

Admittedly, I'm not thinking too hard here to give you numbers, but
you should be able to change the sensitivity of the FM modulator to
achieve this.

Tom



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