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

[Art McBride]

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


-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Henk, PA3GUO
Sent: Wednesday, February 25, 2009 12:21 AM
To: amsat-bb at amsat.org
Cc: pa3guo at amsat.org
Subject: [amsat-bb] Re: GMSK: Time for a stupid question :-)

Thank you to those that replied !

>From the feedback I understand that;
- my TS2000X should be in FM mode, connected to the TNC via ACC2
  (was indeed the case, thanks for confirming)
- my external TNC, the PK-96, should be able to decode GMSK 9k6
  (indeed I can decode AO51's downlink)

So...: I will need to team up with someone else in my footprint
to see how the Cute digipeater (downlink) can be activated. At
this point I have not even heared it, so it can be my ERP
(antenna or RF pwr) or the way my PK-96 is generating GMSK 9k6
signals (vs. how Cute expects them).

Thanks so far, I'll certainly share it if I have more success !
Henk, PA3GUO

> While trying to work Cute-II, I started to think about GMSK ...
> (I have a PK96 external TNC hooked-up)
>
> My beautifull TS2000 has FM/AM/USB/LSB/CW modes.
>
> For GMSK, do I use FM or FSK ?
>
> Please only a gentle smile, I realize I do look silly asking this :-) Henk



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