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

Robert Bruninga bruninga at usna.edu
Mon Sep 27 18:11:41 UTC 2004


>>> wes at johnston.net 9/27/04 11:38:41 AM >>>
>I did some stats with 4 home stations (10 min each) and 
>4 trackers (1 minute each) and came up with... 264 
>seconds out of 3600 seconds per hour, 7.3% utilization
> on 144.99 if everyone in my local area ran 144.39+600.  
>This number is a little higher than Bob's.  But it's in the ballpark.

I'll buy that, but it is a bit high, because it assumes
those 4 trackers are in the area for the full hour.  Either a commute 
is shorter than that, or he traveled out of area..

>>Finally, let's look at your digipeater design ....  Every time 
>>the WIDEn-n side transmits, your local receiver is 
>>desensed and cannot copy anything on the "local" side. 

>Right again.... We either need vertical separation of the 
>144.99 and .39 antennas, or to run cavities.  
>This means we have to double my 7.3% number above 
>to 14%.

AH, but now you are starting to mix apples and oranges.
(deaf trackers versus all other stations).  We need to keep
clear what issue we are talking about here.  I have only
been addressing the alt-freq idea independently of what
kind of station uses it..

>Now if we can forward packets to the digi from the alt 
>input site in such a way that it does not desense the alt 
>input's receiver, we have a winner.

Yes, but this is only an advantage for deaf trackers... not
for regular stations...

>If we end up with multiple alt input digipeaters in a metro 
>area, we need to take care that they can all hear each 
>other.  This is getting convoluted though....  I fear that 
>by trying to cover all the bases and possibilites I am 
>muddying the water.

Yes, keeping it simple is the only way to achieve progress
one digi at a time...  Jumping thorugh all kinds of complexity
and hardware to change an 86% success rate up by
just 7% is just not worth it when the 86% rate is already 
far better than trying to operate a low p ower device on
144.39...

>The maker of the pocket track has said that it will use 
>144.39 and (144.99 or 144.34).  It appears he selected 
>144.34 at the request of a couple of his first customers 
>[for balloons] and because it was close in prox to 144.39.  
>He has offered to sell a pocket tracker on any freq you 
>ask for... so this is really a non-issue.

Yep, that is all we are trying to accomplish here, is to help find
a way to make plenty of more room available on APRS
for these and other local users of APRS.....

>And finally, if CSMA works so well, why did they 
>switch to DAMA in europe?

Good thought wes!   Yes, the missplaced belief that CSMA
works well on simplex AX.25 with shared high-site digis
and low-site users is one of the things that has always held 
back packet from its potential for HAM radio... since day
one in the 1980-'s

good thoughts Wes...
thanks
Bob, Wb4APR





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