[OZAPRS] Sydney

[Owen Duffy]

On 16/10/2014 23:51, Gary Stern wrote:
> Unfortunately,
> there are too many sledgehammers in the Sydney Basin.
> I am about to start looking at a weird way of overcoming that.
>
> I do hope the current crop of 50 Watt aprs, are just not dumb trackers ! 

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.

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.

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.

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.

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.

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.

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.

Will this measure reduce APRS-IS capture of posits? Not much, my article
APRS: how many digi hops to make it to APRS-IS
<http://owenduffy.net/blog/?p=2626> reports that 99% of packets make it
to APRS-IS in one or less digipeater hops.

73
Owen
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