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

Stephen H. Smith wa8lmf2 at aol.com
Thu Oct 20 05:13:54 UTC 2005


jimlux at earthlink.net wrote:

>
> 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.
>
Hello from your next door neighbor!   I'm located in Pasadena about 1 
mile due north of PCC.   ( See http://map.findu.com/wa8lmf   for 
location)  

Several comments on this issue.

1)   RELAY has been discouraged and non-supported in the L.A. area for 
years.  Even before the recent "N-n-only  new paradigm" reconfigurations 
nationally of the last year or so, RELAY was non-grata in SoCal.

2)  Low power mobiles such as handhelds and PocketTrackers on 144.39 
simply don't stand a chance in southern California.  The high-level 
WIDEn-N digis on mountain tops thousands of feet above the basin hear 
thousands and thousands of square miles of the greater L.A. area, and 
are being captured almost constantly by full-power mobiles.   

3)  To reduce the huge number of duplicates resulting from serveral  
high-level digis retransmitting packets already transmitted by another, 
the main wide area digis are now configured as single-hop 
path-truncating digipeaters.    That is, even if a digi hears something 
like WIDE2-2 or WIDE3-3 incoming, it will retransmit the path as a 
used-up string; i.e. *WIDE2-0  or *WIDE3-0 so it won't get any further 
digipeats.   [ If you are monitoring off-air APRS activity with an APRS 
client program that is using current up-to-date symbols (i.e. 
"icons"),   you will notice that the big digi's green stars are now 
overlaid with the digit "1" indicating a single hop 
no-matter-what-path-is-used digi. ]

4)  A WIDE1-1 home "fill-in" located somewhere above Foothill Blvd at 
the upper end of the Crescenta Valley  (Lowell Ave or Tujunga area, or 
perhaps Crescenta Valley Sheriff Sta) would provide a valuble gap filler 
in the "black hole" of the Crescenta Valley blocked from the rest of the 
world by Verdugo Peak.   By placing it at the upper end of the Crescenta 
Valley, you would get a shot at both Oat Mountain (W6SCE-10) at the west 
end of the SFV and  Eaton Canyon (N6EX-3) above eastern Pasadena. 

5)  Bob's suggestion of the "alt-input" digi listening on 144.99 and 
retransmitting on 144.39 would also work nicely from this location.  
Note that 144.99 is not a randomly chosen frequency.  It's what you get 
on transmit  if you set the handheld to 144.39 and turn on the +600 
repeater offset for transmit.  Since the 144.99 receiver doesn't have to 
contend with the RF onslaught from all over SoCal present on 144.39, a 
low-power handheld or PocketTracker actually stands a chance of being 
heard.

6)  I am currently operating an APRS Igate and UI-Webserver monitoring 
144.39 and 30M HF from my QTH in Pasadena.     See
    http://wa8lmf.dyndns.org:14439             for my real-time 
off-the-air maps.   

7)  Contact me with any more questions or setup assistance needed.  



Stephen H. Smith    wa8lmf (at) aol.com   
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://webs.lanset.com/wa8lmf/DigiPaths

Updated APRS Symbol Chart
  http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf   

New/Updated "Rev G" APRS     http://webs.lanset.com/wa8lmf/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:




   




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