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[aprssig] questions on Los Angeles area propagation

Jim Lux jimlux at earthlink.net
Thu Nov 10 05:44:19 UTC 2005


OK.. so I've been fooling around a bit with a low powered tracker (5W into 
either the rubber duck or a trunk lid whip) on my way to and from 
work.  (W6RMK-5 if you're interested) Some interesting observations.

1) There's no good way to tell if you're not getting in because of terrain 
or because of congestion.  Is there some way to look at all the packets 
received and transmitted by one of the high digis (i.e. W6SCE-10)?  From 
that, I could figure out what that digis channel occupancy is, and match it 
up against my presumed transmission attempt times.

2) If I am getting blocked by terrain, the existing coverage of the San 
Fernando Valley is horrid.  We're not talking about windy canyon roads here 
but major freeways cutting across the north and east sides of "the valley", 
the 118 and 210.  I expect to get hidden going through the Verdugo hills 
(about a 5 mile stretch of the 210, and the part of the 210 from Tujunga to 
JPL is a notorious hole, about which something has already been 
discussed.  However, as I traverse that gigantic swath across the northern 
SF valley, which is literally flat as a pancake, I'd expect to have a more 
even distribution of packets into the system.

3) The way the system is currently set up, it appears that the design goal 
is to feed a packet from you, to a high digi, and then to some fortuitous 
Igate.  If I wanted, for instance, to display positions of myself and my 
ham coworkers converging on JPL in an emergency, the existing system 
wouldn't really support that, because there's no way for my packet (which 
most likely goes into W6SCE-10 on Oat Mt) to get to, say, N6EX-3, which 
"sees" Pasadena (although perhaps not JPL, because I can't seem to get a 
packet out from JPL with my mighty 5W tracker).  We are contemplating 
putting in some form of (wide1-1?) digi to improve coverage around JPL, but 
even that wouldn't help much, because people coming in from the north 
wouldn't get picked up by the JPL digi until they are almost on site.

(Well, actually, I could display some of the positions, by using my 
cellphone web browser to go to findu, but it seems antithetical to rely on 
a huge amount of infrastructure provided by others for a tactical system)

4) I've been assured by several folks that if I'd just put more fire in the 
wire, I'd get into the system.  Again, this seems antithetical.. I would 
think that the system should accomodate something one can throw into a 
backpack (with your other junk) and plonk into a rental car without 
worrying about RF safety, starting a fire, draining the battery, 
etc.  Really.. something like a THD7 and a GPS (or, in my case, a Garmin 
GPSIII, a KPC3, and a TH-22)

Anyway, this is all sort of interesting, and I'd be interested to know what 
sort of "network diagnostics" there are to track this down (and even 
better, if there's actually a written description of this somewhere, as 
opposed to tribal lore.  Bear in mind that the SIG archives aren't 
searchable with google)

I'm also going to try an experiment next week.  I have to travel to Goddard 
Space Flight Center in Greenbelt MD, so I'll throw all the stuff in my 
backpack, and if it doesn't look like a IED to the TSA folks, I'll try 
slapping it on and in the rental car.  Maybe it will work better in a 
non-mountainous environment.

Jim, W6RMK





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