In the next 10 years or so we can expect All Amateur voice communications to switch to Digital in preference to SSB or FM. It will be as traumatic a shift as the move from AM to SSB was back in the early 60's.

I don't expect that any of the different Digital Voice systems currently in iuse will be the ones eventually adopted for HF and VHF/UHF - rate of techonological progress can be rapid in this field. But whichever format eventually dominates there will be significant challenges for satellite operation.

When newcomers try out the satellites for the first time they don't use fully computerised doppler correcting set-ups, they compensate for doppler by hand.

Now the existing satellites modes - CW, SSB, FM are all relatively "frequency insensitive" - you can be offtuned by 300 Hz on a CW signal and a human operator will still be able to copy it just fine. SSB is the most critical of the three, but even that can still produce understandable audio even with a 150 Hz+ frequency offset.

All existing Amateur Digital Voice modes are very frequency sensitive, you need to stay within 50 Hz of the correct frequency to decode them and this would be problematic for a LEO sat where the operator is tuning manually.

What we need is a Digital Voice mode that occupies a bandwidth of less than 2.5 kHz, can be decoded with very low S/N ratios (<15 dB) and can tolerate tuning offsets of at least 150 Hz - a tall order but not impossible.

Satellite users need to give some thought to this because unless there is Amateur Satellite Community input to the development of Amateur Digital Voice we could end up with the situation where none of the commercially available Amateur Digital rigs (that's all they'll be in 10 years time) can use LEO Amateur Satellites !

73 Trevor M5AKA

--- Dave hartzell [email protected] wrote:

Interesting idea...

Doppler tracking might also be an issue....do these radios support incremental VFO adjustment via computer control?

73,

Dave NøTGD

On 2/23/07, Patrick Green [email protected] wrote:

...

Hi All,

I'm wondering if the GMSK modulation scheme in D-Star can be inverted and whether the Icom 91AD dualband HT can work full duplex for satellite work. D-Star uses a 6.25kc channel which is way better than the 15kc needed for standard FM but not as friendly as SSB and CW. Let me know. I haven't purchased this equipment but it's worth at least a debate.

73 de Pat --- KA9SCF. _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

-- "It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." - Carl Sagan.

---

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