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

Robbie - WA9INF mwrobertson at comcast.net
Mon Sep 27 20:15:02 UTC 2004

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.


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
> On Sat, 25 Sep 2004 23:11:35 -0500, Robbie - WA9INF wrote:
>>I hope this never takes place on a wide scale. Special events, yes,
>>maybe it may work temporarily without too much detriment to the other
>>To advocate listening on one frequency and transmitting on another
>>without some kind of CD, is asking for some serious kind network
>>I am not aware of any trackers or base stations or digipeaters that do
>>this now. If a tracker can not hear another station or CD, then it has
>>the right to transmit. If a digipeater, or base station, does not hear
>>another station, or NO CD, then it has the right to transmit..
>>But to just blatantly come up and digipeat a low power signal from
>>another frequency with out CD on 144.390, is "intentional interference".
>>It is not Aloha. Isn't Aloha "Transmit if you don't hear another
>>station" and the digipeaters or home RELAYs will sort it out?
>>Even in a busy area like Chicago, I can track several 5 watt trackers
>>when they are on.
>>I hope this can be sorted out before hundreds of stations jump on this
>>without fully understanding what may happen..
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