[amsat-bb] Re: GMSK: Time for a stupid question :-)

Bruce Robertson ve9qrp at gmail.com
Thu Feb 26 04:34:18 PST 2009

On Thu, Feb 26, 2009 at 2:37 AM, Art McBride <kc6uqh at cox.net> wrote:
> Henk,
> I would suggest FM 2.4 KHz deviation. You will need a Gaussian filter after
> the 4800 baud digital to make the logic transitions raised Cosine. The FM
> modulation needs to be direct coupled not AC coupled. Never Had a TS 2000X
> still using a ICom 820 disaster!
> GMSK provide for a modulation index of 0.5 making its performance a little
> worse than AM in performance. Works O K on strong signals, looses it on
> noise, multipath, or interference. There is no capture effect that is
> normally associated with FM and modulation indexes greater than 1
> Good luck,
>  Art, KC6UQH

A follow-on question, if nobody minds.

I've recently bought a Delta-44 soundcard to do some higher definition
SDR work. It looks like the softrock line of radios, for instance,
will have a 2m version fairly soon. http://www.w9idx.com/node/42

What program is state-of-the-art when it comes to digital modes and
SDR work? Or even when it comes to FM audio out, is there a 9600 baud
software sound modem that equals or outperforms a dedicated modem?

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