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Re: AMSAT has a SECRET!



Hi Joe,

I've haven't heard AMSAT say anything specific about digital voice. There
are certainly many text-oriented digital modes that require very little
power and are not any harder to use than RTTY when working DX.

A digital transponder could be designed many ways. One advantage over analog
is that the downlink could be time division multiplexed rather than
frequency division multiplexed. This eliminates the need for an extremely
linear power amplifier and that decreases complexity, increases efficiency,
reduces costs and increases reliability. Think of a time-slot as a frequency
on an analog transponder. Within each time-slot you could have data, voice
or image transmissions. Allocation and size of time slots could be
controlled by the satellite or, in a distributed fashion, by the ground
stations.

If you want the capability for 100 stations to shout over each other in one
time-slot, it won't work well. Plain digital voice would require operators
to function as they do on a FM LEO bird or as AM operators did in the
1950's. However, digital transponders allow much more flexibility.

Each ground station can have access to multiple time-slots for almost no
additional cost. The DX station could be talking to one station on one time
slot while simultaneously receiving the call signs of the other stations
waiting to work him on another time-slot. Call signs from hundreds of
stations can be multiplxed onto one time-slot using a very simple protocol
such as Aloha or slotted-Aloha. Life would be much more enjoyable for
everyone as you could listen to a pleasant exchange between the DX station
and the one station he is working, know that he knows that you are calling
him and wait for him to call you on the voice channel. The DX station can
make many more contacts per hour.

73,

John
KD6OZH
----- Original Message -----
From: Joseph Murray
To: kd6ozh@AMSAT.Org ; amsat-bb@AMSAT.Org
Sent: Friday, 01 June 2001 13:33 UTC
Subject: Re: [amsat-bb] AMSAT has a SECRET!


Hi John

Do you think it possible that digital voice will ever hack a dx pile up .
I have a problem understanding this use of Ham voice modulation .   Can you
help me to understand ?

Joe  K0VTY
===================================================
On Fri, 1 Jun 2001 07:15:21 -0000 "John Stephensen, KD6OZH" <kd6ozh@gte.net>
writes:
> AMSAT-NA did announce the following:
>
> "Third, the Board approved design, construction and demonstration of
> a new
> mode using digital modulation techniques. This would improve
> communications
> under very poor conditions or, alternatively, permit the use of
> lower power
> and/or simple antennas. It is anticipated that both the second and
> third
> projects would be ready to be a part of the main satellite project,
> with
> both a digital modulation system along with traditional SSB/CW
> modulation
> techniques."
>
> Allowing simpler, especially smaller, antennas would be a major
> advantage
> for hams that can't afford the $70 per square foot price of real
> estate in
> Los Angeles. The project may also help amateur radio in the long
> term. The
> FCC made the following statement recently:
>
> "Cross said that before the FCC initiates any rulemaking proceedings
> in the
> Amateur Service to change privileges it wants to see proposals
> involving the
> implementation of "new and more modern communications technologies,"
> such as
> digital".


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