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Re: Why FULLDUPE On is BAD!



Thanks Tim!  I learned something new here!  I fully understand how FULLDUPE 
works, and now
better understand its use for ISS operations.  Here is what you said that 
makes it all clear...

>It simply allows ISS TNC to transmit
>freely as soon as it decodes a good packet...


"Decodes a good packet"...THEN transmits!  I can see where this will work 
at the expense of
other good packets getting in.  Which for now, is BETTER than the current 
situation.

I want to note that changing the callsign (while necessary) will NOT fix 
the current situation or
change ANYTHING.  With its fast orbit, huge footprint, and current set-up, 
ANY communications
(unless private like School Contacts) are going to be hit and miss!  As I 
stated before, crossband
operations with FULLDUPE would make operations better (just like all the 
other sats).

Also, as a hint to everyone, you might have a better chance getting in 
between 0000 and 0600!




At 06:12 PM 04/16/2001 -0500, you wrote:

>"Dino Darling" said:
>
>
> >
> > IF it is TRANSMITTING, then it can't RECEIVE.  IF the TNC was set up in
> > FULLDUPE, then
> > the TNC would FORCE the radio to STOP listening in order to TRANSMIT by
> > virtue of cutting
> > off the receiver (in spite of its nose?).
> >
> > How then, can the TNC (via the radio) re-transmit what it cannot
> > hear?  Maybe FM in space is
> > SUPER MAGIC!
> >
>
>No magic in that space dust...
>
>You are correct, Full Duplex mode is typically used when you have a separate
>transmitter and a receiver that can work in the full duplex mode (i.e.
>receive
>while transmitting simultaneously unlike the ISS setup).
>
>This issue is that the TNC will not freely digipeat a packet on the in-band
>downlink in the simplex mode when there is a lot of packet traffic feeding
>the uplink.  In this case, a timer in the firmware must time-out before the
>unit
>will transmit.  With Full Duplex mode activated on the TNC, the transmitter
>will transmit on the downlink immediately at the expense of missing any
>data coming in the in-band uplink channel as it transmits for a brief
>period.
>This is not a big deal since may of the packets are not being decoded from
>  the high concentration of signals being received on the input.  That in
>itself
>is the reason why you do not hear the ISS TNC transmitting frequently.  So,
>Full Duplex does nothing for this common problem.  However, Full Duplex
>does allow the TNC to transmit without waiting for the time-out function to
>expire for the busy channel indication.  It simply allows ISS TNC to
>transmit
>freely as soon as it decodes a good packet instead of being delayed by the
>timer function due to a busy channel.  The channel will always be busy in
>space with the number of stations appearing in a footprint containing a
>large population.
>
>It is really no big deal in any case, but may be helpful in improving the
>efficiency.
>
>If you listen to the amount of noise and activity on Amateur Satellite UO-14
>and AO-27 when they are over a populated area you would get a small
>sample of what the level of noise would sound like on the ISS.  I emphasize
>that this would be a small sample of the reality.
>
>
>
>
>73's,
>
>Tim - N8DEU
>Huntsville, Alabama
>
>
>
>----
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Dino...k6rix@arrl.net

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