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[aprssig] Object DENNI_ato Cannot Be Seen on RF Path

Wes Johnston aprs at kd4rdb.com
Sun Jul 10 23:24:21 UTC 2005

At the risk of starting a bunch of hate and discontent (Geoff, you know
I'd never rain on your parade ;-) ), You can only fit 5lbs of poo in a
5lbs sack.  1200 baud is going to be a trade off... you (the group in
Florida) will have to choose between a RELIABLE network and a network
that can show stations in a "catch as catch can" fashion.  Personally, I
prefer a RELIABLE network that allows me a fair shot at hitting my local
digipeater.  As much as you'd like to see where the hurricaine is, it's
not headed your way.... and the NWS plots positions +12, +24 and +36
hours, and if one of those positions lands on your local area, your
local IGATE should gate it out.  That gets us into a situation where you
gotta have an IGATE nearby.  Funny thing is that when people mention
IGATE they automatically think internet.  The aprs internet feed could
come in over a much higher bandwidth internet connection over TNOS or
JNOS on 70cm or higher.... or you could work with a local hosptial,
police or emergency ops center that has redundant internet access and
use them for the IGATE.  Everything is a compromise and it seems we are
stuck at 1200 baud for the sake of mobile stations, so we gotta live
within the contraints of a 1200 baud channel.  I visited Tampa 6 or 7
years ago and remember it was a saturated mess that was unreliable.

Here's another idea that can use off the shelf tech....

Something that would be really slick would be to move to 9600 (which the
kenwoods can do) on 70cm.  Run a split frequency (like the alt input on
144.99/144.39)... So you still get position reports from tiny tracks and
the like from 2m 1200 baud.  The local digi would do nothing but keydown
all day and send loads of data at 9600, meanwhile listening for 9k6
inputs on another 70cm frequency, and also collecting positions and
objects heard on 144.39 and digipeating them on 440.  The locals heard
on 70cm input and 144.39 would be mixed in with other data on 70cm.  You
gain a whole bunch of bandwidth once you get rid of TXDelay on 9600 by
simply keeping the transmitter keyed for extended periods of time.  Bob
even has a page that describes linking cities on 9600 baud.  Thing is,
by carefully coordinating the 70cm output frequencies, other towns could
hear your 70cm transmitter and you theirs.  The trick is to get away
from simplex frequencies.  By all means still support 144.39 on a local
level... but the locals know what their local 70cm frequency is and they
will see loads mode when they listen to 70cm. 

See http://www.kd4rdb.com/kd4rdb/Backbone%20routing.ppt for some older


Geoffrey Dick wrote:

>Thank you for clear explanation about IGATE permissions, but this 
>is about the RF path !   In the area regard, there may be no IGATES
>because telephone and power utilities will be out.   We are talking
>of a widespread area where APRS might we of use via RF ONLY.
>I experienced this last year working communications in shelters 
>during 3 hurricance passing through Central Florida.   We really
>need those long RF paths !!!!!   Wide2-2 will simply not cut it.
>Kind regards,
>Geoffrey Dick, wa4ikq
>aprssig mailing list
>aprssig at lists.tapr.org

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