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Re: TDMA - Reading the mail



on 12/21/00 5:20 PM, Greg Preston at preston@telia.com wrote:

> Hey Jon,
> 
> The way I see it, the ground station would press the key on the mic and their
> callsign would be digitally uplinked.  The satellite would then relay each
> call
> sign to ALL stations and those calls would appear on the rig's display.
> P51AAA
> would run down the list as they come in, or any way he or she would like.


But this would only work given the assumption that the satellite or the
receiving station can properly demodulate the digital signals!  If due to
the high number of stations, you don't get a properly decoded call sign what
good is all of the whiz bangs in the world.  In the analog world, I can hear
half a word and my brain knows what the transmitting station is saying.  In
the digital world, if half of a "word" is missing, it demodulates nothing.
It's an all or nothing situation.  So when you have high densities of users
all clamoring to use the same channel, then the system breaks down.  You are
assuming an orderly system.

Such things can be done over the internet as you suggest because bandwidths
are very wide and so are speeds.  Over a satellite link, you have narrow
bandwidth compared to terrestrial line and you have slower data speeds.

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Member:  ARRL, AMSAT, DXCC, NRA

http://www.qsl.net/ke9na

"A life lived in fear is a life half lived."

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