Hi Henk
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 ?
FM. FSK is for (relatively) narrow band RTTY type modes that traditionally you'd have your radio set to USB or LSB. Your TNC modem will expect the signal to have gone through a limiter/discriminator, so you need the TS-2000's FM mode.
GMSK is FSK, but with two particular features.
Firstly the modulation index for GMSK is always 0.5, with state changes occurring at zero crossings and phase continuity maintained. Secondly, after the scrambler, the 1's and 0's go through a Gaussian filter and that's what modulates the FM carrier: the -3dB point of that Gaussian filter is determined by the BT.
The primary benefit of GMSK is that it reduces adjacent channel interference at the expense of intersymbol interference. I doubt that;'s the reason it was chosen for this mission though, much more klikely it was because you can buy chips off the shelf to do GMSK.
There's quite a good intro to GMSK here http://sss-mag.com/pdf/gmsk_tut.pdf
So yes, you should be able to demodulate GMSK with a standard 9k6 G3RUH modem although theoretically it might not be optimal.
73, Howard G6LVB