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Re: PCSAT2 Digipeater 2 hops

I should have thought about the parallel to terrestrial use myself...thanks 
for taking the time to explain this...


----- Original Message ----- 
From: "Robert Bruninga" <bruninga@usna.edu>
To: <amsat-bb@amsat.org>; <rogerkola@aol.com>; <vk4tec@tech-software.net>
Sent: Thursday, September 01, 2005 12:36 PM
Subject: Re: [amsat-bb] PCSAT2 Digipeater 2 hops

>>> "Roger Kolakowski" <rogerkola@aol.com> 09/01/05 7:18 AM
>In this setup, it looks like one "end" of the ISS
>is transmitting on 145.800 and the other "end"
>is receiving on 145.825, only 25 kHz apart?
>Is this enough separation?

No, and yes.
This is AX.25 packet which is a low-dutycycle
mode for amateur radio.  That is, the 145.800
transmitter will block the 145.825 receiver
for 1 second or so now and then, but this is
no different from the kinds of collisions that
happen all the time on a shared channel.

Lets say the user support capacity for one
digipeater is X.  For 2 totally independent
digipeaters on separate bands and without
any interference would then be X+X or 2X.
(twice the capacity).

Now lets say that the TX dutycycle of each is 10% TX
and 90% RX and that one of  these (145.8) blocks
the other when it transmits.   Now then the total
capacity is now 1X + .9X or 1.9X.  This is less than the
possible 2X, but still better than 1X.

Even if they were both on the same band and both
blocked each other, it is easy to see that the
combined throughput would still be 1.8X.  So we
are not that concerned about the blockage.

But someone wanting to have a better probability
of getting through PCSAT2, might want to listend
to 145.8000 with an HT and avoid transmitting
when the 145.800 is transmitting.

But this shows why in the future, we want to
get all ARISS experiments to transmit on only
one band and to have all inputs on anonther
band to avoid these kinds of blockages.

de WB4APR, Bob
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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