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

Wes Johnston wes at johnston.net
Mon Sep 27 19:38:34 UTC 2004


Thing is (and I'm agreeing with you to a point) ... I am in a different part of town (or even one mile away from my buddy with a d700), and we don't hear the same stations.... I hear something off in the distance that keeps me by seizing that 2 second spot.  His station may or may not hear that same DX station I hear, so he goes for the 2 second lull.  Still, the CD indicator on my tnc serves to randomize our Tx timing.  I do worry about just what you say though... if we can only hear the local digi (nothing else in the distance), we could attempt to seize the digi at the same time.... but the chances of that are just as slim as us being on opposite sides of town and unable to hear oneanther under the CSMA rules.  In the end, neither Aloha or CSMA is perfect.  Depending on the user's antenna height, one or the other will be more advantageous to a portion of the users.  Bob is just trying to give the ones at a disadvantage under CSMA a place to go.

Wes


----- Original Message -----
From: "AE5PL Lists" <HamLists at ametx.com>
Date: Mon, 27 Sep 2004 13:44:55 -0500
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
Subject: RE: [aprssig] APRS low-power-local ALT input channel
> By the way, regarding a comment you made earlier in your post, if two
> D700's are using the 144.99/144.39 approach with CD on 144.39, you have
> increased your chance of collisions markedly in a heavy use area because
> they both will go for the same 2 second dead spot and neither will have
> the benefit of recognizing that the other has started transmitting.
> There will always be some small variances in the timing between rigs
> which could be made use of in a simplex operation, but not in this mode.
> 
> 73,
> 
> Pete Loveall AE5PL
> mailto:pete at ae5pl.net 
> 
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> aprssig at lists.tapr.org
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