[aprssig] Digital two-way Radio communication in emergency situations

andrewemt andrewemt at hotmail.com
Mon Sep 8 16:01:31 EDT 2014

Uh, if the digi (as opposed to a human administrator) specifies the timeslot for each tracker, then those trackers have to be two-way (not transmit-only) in order to be able to hear their assignments. Pretty much eliminates all current dedicated trackers, since they can't receive.

And, as you point out, you still have the hidden transmitter problem if you have any central authority (such as your suggested digi) handing out slot assignments, and it can't hear every tracker.

Split frequencies only help a little if there is no coordination among all the trackers, and the digis will just copy the chaos to their output frequency.

Assuming we _can_ get two-way trackers that can listen for assignments, is the AIS protocol still patented somewhere in the world (despite the US government overturning the patent in the US)? I wouldn't want to implement something that would get some users in trouble due to patent infringement.

Just wondering if it's worth trying to implement a dynamic time-slotting (as opposed to the existing static time-slotting the transmit-only trackers use), and whether it could successfully coexist with existing legacy transmit-whenever-I-want-to units.

Andrew, KA2DDO

-------- Original message --------
From: Scott Miller <scott at opentrac.org>
Date:09/08/2014  13:53  (GMT-05:00)
To: TAPR APRS Mailing List <aprssig at tapr.org>
Subject: Re: [aprssig] Digital two-way Radio communication in emergency situations

On 9/8/2014 9:20 AM, Robert Bruninga wrote:
>> A new network ought to allow only users with... coordination
> capabilities.
>> You don't get to transmit without knowing the exact time... [slot]
>> The tricky part is coordinating slot reuse between overlapping digis...
> An easy fix for purpose built nets for special events is to eliminate that
> problem by using split freqs.  One for the trackers and the other for the
> digi outputs.  Just like we do here for local special events.  144.39 for
> digi outputs (so everyone can see everything and everyone) and +600 for
> tracker inputs.

That's not exactly what I meant... though for the Burning Man project I
was working on slotted digis that would aggregate traffic over a 5
second period and transmit everything within a dedicated 1-second digi slot.

The problem I'm talking about is if you have a digi acting as a channel
access control authority and assigning slots to trackers.  You don't
want the same slot on the same channel being used by different trackers
in overlapping digi coverage areas.


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