[aprssig] APRS low-power-local ALT input channel

J. Gary Bender, WS5N WS5N at mindspring.com
Mon Sep 27 18:21:02 CDT 2004

Hi Robbie,
Perhaps I misinterpreted the specs for devices like PocketTracker. 
 I was under the impression they do not have receivers.  As transmit-only 
devices, I assumed they are not aware of activity on channel.  If I am wrong, I
(happily) stand corrected.

It looked to me that Bob clearly stated that an ALT input would be an additional 
input to an existing TX/RX .39 digi.  Such a digi listens to .39 AND the ALT 
input, but only transmits on .39.  I think we are all in agreement that simply 
cross-frequency digipeating would not accomplish anything positive.  

Gary, WS5N

On Mon, 27 Sep 2004 15:15:02 -0500, Robbie - WA9INF wrote:
> Hi J. Gary,
> Out of curiosity, what trackers are "deaf"? If you mean they don't
> decode a packet, true, but all the ones I know about have at least CD..
> Blindly transmitting was in reference to a ALT channel digi that would
> listen on 144.990 or any other frequency except 144.390, and digi on
> 144.390. Without CD on 144.390, I call that "blindly transmitting".
> Bob says we do it all the time on the voice repeaters, so I guess that
> makes it right for the ALT channel idea.. Oh well. I'll back out of it
> and let it fall where it may.
> Robbie
> J. Gary Bender, WS5N wrote:
>> I think you are ignoring the fact that DIGIpeaters are not real-time
>> REpeaters.  They are store and forward devices.  It is SOP for
>> packets, received from any source, to be stored on-board the
>> digipeater until it is able to transmit on a clear channel.  I doubt
>> that the thought of digipeating on to .39 blindly was ever considered -
>> - it just is not the way the machines work.
>> The alt/input 144.99 proposal is a collision avoidance device in it's
>> own right.  It is a good and workable engineering compromise.  It puts
>> the most susceptible devices, and most likely to collide, on a channel
>> with a much lighter load and no high power stations.
>> One of the reasons I abandoned packet 10 years ago was because of the
>> "hidden station" problem.  APRS, because it took the limitations of a
>> simplex network into account, works fine in that environment.  I was
>> taken aback when I saw deaf trackers so popular on APRS -- however, if
>> the network could not handle them, they would not be so popular.  This
>> proposal gives the little trackers a much better chance. -- J. Gary
>> Bender, WS5N Tijeras, New Mexico  USA

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