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<div class="moz-cite-prefix">On 16/10/2014 23:51, Gary Stern wrote:<br>
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<blockquote cite="mid:543FBF39.5040501@gmail.com" type="cite">Unfortunately,
<br>
there are too many sledgehammers in the Sydney Basin.
<br>
I am about to start looking at a weird way of overcoming that.
<br>
<br>
I do hope the current crop of 50 Watt aprs, are just not dumb
trackers !
</blockquote>
<br>
Last point first, dumb (I assume you mean fixed period beacons,
especially set to short periods and stationary) trackers are a
problem at any power level as they increase the risk of collision
and lost packets for little benefit. Until a week ago, one
stationary tracker 85km away accounted for 15% of the packets heard
in a day at my location.<br>
<br>
Sydney is an interesting scenario, it has no prominent digipeaters
within the metro but depends on three prominent digis 40-60km from
the metro centre (VK2RAG-1, VK2AMW-1, VK2RHR-1) and several iGates
with somewhat local coverage (though they all hear several of the
aforementioned digis.<br>
<br>
So, a Sydney mobile tracker signal is not rock crushing at any of
these digis due to distance, and it is likely that another tracker,
not hearing an current tracker transmission due to distance and
topography transmits at the same time, and one or both packets may
be damaged and discarded at one or more of the three digis. So the
chances of a transmitted packet being decoded directly by one of the
igates, or decoded by a digi, repeated and decoded by an iGate are
well less than 100%, and the probability diminishes with increasing
traffic.<br>
<br>
If that looks bad, consider that those three prominent digis hear
several other digis very well and so, not only are trackers in
Sydney competing against each other, but against digi traffic from
Tamworth, Newcastle, Orange, Canberra etc. In fact, the three digis
(VK2RAG-1, VK2AMW-1, VK2RHR-1) all carry traffic from these outer
digis further increasing the traffic level in the Sydney area.<br>
<br>
Traffic is the enemy of trackers, whether it is other trackers
locally, trackers mindlessly iGated from IS to RF, trackers
needlessly digipeated from out of area, weather beacons, messaging
etc... all these compromise position reporting performance.<br>
<br>
Hams are still muttering "New N Paradigm" a decade after that mid
life kicker was promulgated, it is time for lateral thinking instead
of blindly following Bob. Bob's packet fratricide is not the answer
to Sydney's challenge.<br>
<br>
I understand that one digi operator is showing leadership in this
mess. I hear that the Goulburn and Southern Highlands Amateur Radio
Club intend changing VK2RHR-1 so that it will not repeat any packets
that have already been repeated. I estimate that measure will reduce
its transmit rate by around 30%, and although that is only a
fraction of the total Sydney traffic, the benefits should be felt my
not only travellers along the Hume through the area, but by all of
Sydney and digis out to Canberra, Tamworth and Newcastle and their
users that will enjoy less congestion.<br>
<br>
Will this measure reduce APRS-IS capture of posits? Not much, my
article <a href="http://owenduffy.net/blog/?p=2626">APRS: how many
digi hops to make it to APRS-IS</a> reports that 99% of packets
make it to APRS-IS in one or less digipeater hops.<br>
<br>
73<br>
Owen<br>
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