[aprssig] Questions about being both an iGate and digipeater.

Bob Bruninga bruninga at usna.edu
Thu Jul 21 09:41:40 EDT 2011


> I do a digipeat and Igate here in Eureka too.  
> However, I have a delay set on my digipeat function 
> which keeps my station from doubling with
> other stations.

Actually, it does the opposite.  It increases your digi's chance of doubling
with another user and another person's packet.  

All digipeaters in APRS are supposed to have DWAIT set to 0 so that all
digis that hear a packet all transmit at ONCE.  This makes sure that all of
those 2, 3 or 4 copies of the packet all take up only one SLOT time, not 4.

Sure they all collide with each other, but for the users that are closest to
each one of them, they will get a more powerful copy from their closest
digi, and will receive it just fine.  Similarly, outward rings of
digipeaters will also only hear a stronger copy and so there is no loss of
outgoing radial packets either.

Sure there are geometries where there are equal power collisions, but these
are small areas, and far less of a concern than allwign digipeaters to
multiply QRM by factors of 2, 3 or 4 by delaying. 

If an individual's station just happens to be perfectly between two
digipeters and therefore always hears a double that is not decoded, then he
should move his APRS antenna to one side of his house to "favor one digi by
about 10 dB over the other".  That way, one will always win.

An exception to the above is out in a huge wilderness area where there are
so few  users and digipeaters, that the channel is say quiet 9 seconds out
of every 10.  Then the added dupes might be OK.  But do not forget that you
have set this DWAIT landmine later when activity increases and then all the
dupes arr blocking other users packets.


73 and good luck

On 07/20/2011 06:41 PM, Matthew Schumacher wrote:
> Hello all,
> I'm a bit new to ham/aprs, but I want to start tracking my airplane so I
> decided to setup a digipeater to contribute (I live in Alaska in a place
> where I'm 30-40 miles away from the nearest digipeater in one direction
> and hundreds of miles the other direction.)
> At first I setup both an iGate and a digipeater, but when I was looking
> in my logs, I would find situations where I would digipeat and another
> station 30 miles south of me would digipeat at the same time, and
> quickly enough so that the WIDE number wasn't decremented so the next
> hop was transmitted twice, but thankfully not at the exact same time on
> the radio.
> After seeing that I'm just not seeing a point in being a digipeater and
> an Igate at the same time so I disabled the digipeater.  Unless someone
> is looking for aprs information on the radio channel why digipeat when
> the data is sent to the internet and made available there.
> I can see why you would want to digipeat if you didn't have internet
> access to get around a hill or cover some other remote dead spot, but
> why tie up more RF if everyone is going to look to the internet to pull
> up the information.
> Am I missing something here are do others feel the same way I do?
> schu
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wishing you well
Jaye, ke6sls--via the acer w/thunderchicken3

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