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[aprssig] setting up digipeaters & I-gates

Stephen H. Smith wa8lmf2 at aol.com
Fri Jul 23 19:46:53 UTC 2010

  On 7/23/2010 10:58 AM, Jaye Inabnit ke6sls wrote:
> i Stephen:
> I'm not sure how you might have interpreted my questions regarding I-gates and
> Digipeaters as confusing the two--I have a good grasp of packet as I
> mentioned in my original post.

However, APRS differs from classical packet in three very major ways:

*ALL*   APRS operations are done in UI-Frame unconnected mode -- you never 
"connect" with another station.    In classic packet, UI mode was used mainly 
for beacons and the occasional "roundtable" net-type operation.

All APRS digipeaters use the same generic "callsigns"; i.e. WIDEn-N rather than 
specific calls as classic packet did.   As a result, the APRS digipeating 
process "floods" out in every direction from the originating station in an 
ever-widening circle, rather than following a linear path defined by specific 

Classical packet never had the issue of RF<-->Internet connections.

> The link you included was very helpful.  I just finished reading it and have
> as many questions as I did before reading--which in my case is a good
> thing :)
> Now that I'm back at my QTH, I want to start defining good hill top gear--KPC
> by Kantronics seems like a good choice but I'd certainly like to hear what
> other node operators are using on their hill tops.

In terms of simplicity, minimal space and minimal power consumption, it's hard 
to beat a radio & KPC3+ as a stand-alone digipeater.   Not having a PC on a 
remote mountaintop is a real advantage, both in terms of power consumption, 
space and potential software problems & lockups that require reboots.

The KPC+ draws less than 15mA at 12 VDC if you disable the panel leds.    It 
will work with virtually any VHF radio.   KPC3 can output very high TX audio 
levels ( greater than 1 volt) which is essential if you use old commercial LMR 
radios like GE Mastr IIs or Motorola Micors which have very high mic-input 
levels; i.e. telephone line-level equivalent.

(If your are going to be sharing mountain tops with public safety and 
commercial land mobile users, it's almost essential to use commercial-class 
radios.  The receiver front-ends of most ham gear will be grossly desensitized, 
blocked or intermodulated when exposed to the nearby RF onslaught on a crowded 
mountaintop site. It's like a field-day multi-TX scenario only 50 times worse!)

If you pick them up second-hand, be sure you get KPC3+, not the earlier KPC3.   
The older KPC3 uses an entirely different CPU; firmware updates are not 
available for it.   New KPC3+ units come with firmware compatible with the most 
recent APRS standards, and older Plus units can be updated to current.

Or you might want to consider some of the newer-generation far less expensive 
"mini-TNCs" such as the TNC-X with it's piggyback digipeater board


Or the Tracker 2 from Argent Data


Or the TinyTrack 4 from Byonics


All of these differ from "classic" TNCs by not having the traditional 
command-line interface and interpreter intended for use with early 
1980s-vintage dumb terminal devices.   They present basically a KISS-type 
interface to external computer programs.

> Here, I have access to
> some VERY good locations--locations that are very much needed since this is
> serious canyon country.  We are a responsive ham group here on the coast, so
> I will certainly have plenty of good help too.  Anyway, I'd like to use gear
> that is future compatible (non-locked in firmware etc) so updates to APRS
> routing can be facilitated without replacement of costly gear.
> I think I'll set up an Igate here at my QTH.  I only use Linux so any Igate
> ops lurking, please feel free to post suggestions/help/tips via this list.
> Just a quick perview of Igate software available looks interesting, however,
> I will need to read much more about it since I don't want to listen to
> traffic as much as I wish to add "our" traffic to the APRS servers.
> I've been sending packets for over 12 hours and yet to have any heard by an
> Igate using 5 watts and a very high gain antenna.

Are  your sending your packets to a destination beginning "APxxxx" ?    Do you 
have your coordinates in proper format as part of the transmission?

Except for a few special exceptions, such as the mic-E compressed format where 
part of the location data is compressed into the destination field,  igates 
will ignore any packets not addressed to "AP-something".    Further, nothing is 
going to appear on a map unless you send your own lat/long (correctly) first.

Of course, the RF absorption losses of redwoods are considerable!

> It's very clear I need to
> get a hill top digipeater in place to cover the towns of
> Trinidad>Mckinleyville>Arcata>Eureka>Loleta>Fortuna>Rio Dell (These towns
> account for most activity and usually can't hear each other even though
> distance is relatively small).  These towns are 0n HW101.
> Finally, are backbones used for APRS via local digipeaters?
In most places, NO.    The vast majority of APRS activity is peer-to-peer 
non-hierarchic 1200 baud operation using whatever other stations happen to be 
within earshot.

In a few places, yes.  The Pacific Northwest (Oregon, Washington, British 
Columbia) have a quite sophisticated 9600 baud backbone for the 1200 baud 
"users' system".

> I'd really like
> to see how other communities like ours are set up to handle the difficult
> terrain.  Relieving packet dups/congestion at 1200 packet speed is obviously
> very important.
In an area of relatively low population density and high RF losses (forests and 
not-terribly-high mountains), I doubt that congestion will be a major problem 
for you.

  [It's  a far far bigger problem in the central valley along I-5 and CA-99 
where digipeaters on very high peaks in the Coastal Ranges and the High Sierras 
have minimum-loss line-of-sight paths of sometimes a hundreds miles or more to 
major population centers like the Bay Area, Sacramento-Stockton, 
Merced-Modesto, Bakersfield, and over the Tehachapis to the greater L.A. area. ]



Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      WA8LMF  or 14400    [Think bottom of the 2M band]
Skype:        WA8LMF
Home Page:          http://wa8lmf.net

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