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[aprssig] Question about low power APRS in Los Angeles area

Jim Lux jimlux at earthlink.net
Wed Oct 19 23:37:25 UTC 2005


On behalf of Courtney N5BF, I am forwarding this for comments and potential 
answers.  I've inserted some additional information in the middle (in 
square brackets) to clarify certain local aspects.  Here's some background 
geographical information too:

The JPL Amateur Radio Club (JPLARC, W6VIO) has a 220 and 440 repeater on 
Cerro Negro, which is a hill that has a view of downtown LA as well as La 
Canada. Coverage map at:
http://wr6jpl.ampr.org/cn_lcf.html
We also have a 2m site up on the JPL Mesa Antenna range above the lab. 
Coverage map is at: http://wr6jpl.ampr.org/jpl_mesa.html
And, the references to 180 refer to a 9 story building at the West end of 
the lab where we have a shack on the roof with some UHF and VHF equipment 
(and a network connection)
If you look at the picture here: 
http://www.jpl.nasa.gov/about_JPL/images/jpl-browse.jpg
Bldg 180 is the tall slab-like building at the left side of the picture 
with vertical white stripes.  That picture also shows the Mesa antenna 
range along the ridgeline directly behind the lab.

The N6EX repeater is some 5 miles to the east.

From: "Courtney B. Duncan" <courtney.b.duncan  AT jpl.nasa.gov>
Subject: APRS in Canada/Crescenta
To: James.P.Lux  AT  jpl.nasa.gov

Local guidelines for APRS use recommend WIDE2-2 as the best path in 
SoCal.  I observe that this is true for mobiles running something like 25 
watts to an outside antenna, even up here in our little valley.

I now have experimental evidence that Bicycle or Hiking mobiles (think "HT 
on high power") in this area are not well served.  In half a dozen 30-60 
minute bicycling trips through the hills and vales west of JPL, I've 
managed to get an average of one packet into the network per trip, 
something like a 3% success rate.  Clearly this won't do.

Running 25 watts bicycle mobile is problematic and is not a good "routine" 
solution.

Mild research on this subject leads me to believe that using an alternative 
path of WIDE1-1,WIDE2-1, or RELAY,WIDE2-1, would help me, as a QRP user, by 
activating localized digis that are meant to fill in holes like ours.  I 
could easily install one of these at my house, but my house doesn't have 
good views into the Crescenta/Canada valley either.  I'm in that hole on 
the 210 at the Ocean View exit where you start to lose the JPL 2 meter 
repeater [up on the Mesa antenna range] while westbound.  KK6PD operates a 
RELAY further west, but he is in a worse location than me, nearly under the 
freeway near Lowell right before you lose all JPL repeaters westbound.  We 
don't need something very high up to help in the valley here, but we do 
need something that is not at the bottom of a debris basin as KK6PD and I are.

I note from my (car) mobile trip raw data that none of the big WIDEn-N 
stations (the N6EXs and others) are closer than about 20 miles from us 
here.  Though La Crescenta is the "back porch of L.A.", our blockage to the 
south gives the area unique problems in this network.  Like I said, 25 
watts mobile works fine, HT on high power barely works at all.

 From my perspective, one of those big N6EX WIDEn-N stations on Lukens or 
Cerro Negro would totally fix this.  From an L.A. basin network planning 
perspective, however, this might add too much node crowding. (I don't know 
this, I'm just speculating.)  From my personal perspective, a WIDE1-1 digi 
in our Building 180 shack, or at the 147.15 site or on the Lund building up 
in La Canada would fix it too.

An aside.  It looks like the modern recommendation is to set up localized 
digis with WIDE1-1 for this.  It also looks like, from my study of packet 
traces that I can see from my house, that if one of the big WIDEn-N guys 
sees you, even though you have RELAY in your path and even though you 
haven't been repeated by RELAY*, he will still pick you up and do the next 
thing, like WIDE2-1.  If this is true, then my QRP station should always 
run WIDE1-1,WIDE2-1 so that if seen either by a localized digi or by 
WIDEn-N, I'm in.  But, it wouldn't help around here because right now there 
are no WIDE1-1 digis.  Using RELAY,WIDE2-1 would work except I lose KK6PD, 
the only local RELAY, when I turn left out of my driveway.

So, here's the question.  If the club ran a 144.39 radio at Cerro Negro, on 
the mesa, or on top of 180, would we configure it for digi use by local QRP 
stations and if so, how?  Or, would it make sense for it to be a WIDEn-N 
node?  In terms of the SoCal network, what would be our preferred location 
and configuration?  What kind of installation makes the most sense in terms 
of our service to the local valley, my own problem notwithstanding?

Does the club have old (or new) radios and TNCs sitting around that could 
be put into this service? [We probably do.] If it's just a matter of making 
a cable or loading some software or something, I'd be happy to work on 
it.  If it means installing something new on Cerro Negro, that's probably a 
broader effort.[We have limited access to the repeater site on Cerro Negro, 
and limited room once you get there]

Courtney

OK all you APRS gurus.... what's the best solution for Courtney's 
problem... directional antennas?  Beaconing every 0.5 seconds? Microwave 
transmission of power to Courtney as he bikes through the hills (keeps him 
warm AND connected simultaneously)?

http://www.findu.com/cgi-bin/find.cgi?call=n5bf-3&terra=4
http://www.findu.com/cgi-bin/find.cgi?call=n5bf-4&terra=4

Jim, W6RMK






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