[OZAPRS] Scenario

Brian Beamish bbeamish at bigpond.net.au
Sat May 29 23:19:09 EST 2004

Hi Folks
Firstly Richard thanks for all your effort will watch out tomorrow,
Sunday, although I have to be away from home for a while taking the XYL to
a craft show, no APRS there that is for sure but one of those things one
has to do once in a while pleases the XYL to have me along showing a lot
of interest as well. Richard will check it out when I can.
Whilst not a member of WICEN both I and Des VK4DMI-4 do help them out when
ever possible and realise from seeing the use they have made of VHF APRS
just how valuable it could be in an emergency situation. 
On HF it could particularly in country be quite an asset in a similar
situation it would seem from a couple of the messages floating around on
OZAPRS and else where that some do not quite realise some of the
differences and difficulties getting beacons through on HF.
For example a beacon sent on VHF will take around 4 times longer so send
on HF if that beacon is digipeated with the slight gap between the
original and digipeated signal it will take around 10 times as long as
Imagine that you have 4 gateways beaconing say every 15-30 minutes
hopefully not all at the exact same time and you are out in the field with
say 5-6 mobiles that beacon say every 5 minutes hopefully not at the same
time or at the same time as the gateways with digipeating NOT taking place
and you could do impossible by coordinating each mobile and/or gateway to
beacon at a slightly different time not on top of each other you would
possibly would get most beacons through.
Now throw in gateways digipeating this would double the traffic 4 gateways
digipeating would be equivalent to 10 gateways (2-3 delay between original
and digipeated signal) the 5-6 mobiles would have their beacon effectively
doubled by the digipeating with all this going you would soon give the
game away as you would have more luck winning the lotto than getting a
beacons through.
The above presumes as would be the case I hope in an emergency that all
others would stay off the frequency.
If you want to reduce the number of mobiles able to operate in the limited
space and only see gateways go for it start digipeating but if you want to
see a HF APRS network grow, as it will Terry, and work as it should let
Richard work at sorting out the problem as he is currently trying and will
eventually do.
Off to bed here
 B C N U
Brian VK4BBS
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