16775Re: [tracker2] Macro issues OT3m
- Aug 16 10:35 PMI think I should just hire you to do all of my customer service, James! You're beating me to all of these. =]
On 8/16/2014 9:45 PM, James Ewen ve6srv@... [tracker2] wrote:
From your recent posts on this forum, it looks like you're very new
into APRS and and still have some very idealistic concepts about how
this is all supposed to work. I used to be just like you... give me a
little while, and I'll try and beat this optimism out of you. If I
succeed, I might be allowed to join the "club".
On Sat, Aug 16, 2014 at 9:23 PM, owenvk@... [tracker2]
> "Digipeaters are supposed to immediately grab the channel and digipeat what
> they heard."I have noticed in my recent exploration of APRS that digis tend to
> "immediately grab the channel", and I am sure some lightweight thinkers have
> put forward rationale for this...
Well, the primary "lightweight thinker" behind this concept is Bob
Bruninga WB4APR, the guy that invented APRS.
Have a Google for APRS packet fratricide. Bob's concept is that
neighbouring digipeaters are SUPPOSED to intentionally interfere with
each other, and in doing so, they stop packets from propagating over
large distances. It's a ridiculous idea, and to attempt to be able to
make it work, you have to expend a great deal of time and effort to
find locations for digipeaters that would allow such a concept to
I've butted heads with Bob a number of times over basic concepts like
this. I put forth a concept to Bob back in 2002 about dynamic
digipeating that would limit the packets digipeated based on the
number of packet digipeats being requested, and the distance of the
source station. That was dismissed as being bad for APRS because of
the "randomness and unpredictability" of the digipeating of packets.
Yet this packet fratricide concept is deemed to be APRS nirvana.
> but for example, there are two WIDE digis on very prominent hills. both within 20km of my
> home and can be heard for hundreds of km... and when they both "immediately grab the
> channel", they interfere with each other and you are unlikely to decode either of them.
Hey, sounds familiar, huh? That's how APRS is "supposed to work".
Packet fratricide is working perfectly.
> It is one of the contibutions to low success rates in getting posits to a remote iGate that hears both digis.
But, by design this is EXACTLY how the digipeater network is supposed
to work. Bob's suggested solution is to put a yagi on the i-gate so
that it receives one digipeater stronger than the other. By getting
one signal stronger than the other by a large enough margin, the FM
capture effect will allow for a successful packet decode.
Your local digipeaters are not installed properly to be able to
support digipeating in the APRS network. One or the other would need
to be relocated so that you don't get the overlap where you see the
collisions. Yes, that's a pain in the backside, and it is very
difficult to find locations where you can get the digipeaters set up
to provide unique coverage, yet still be able to talk to the
neighboring digipeaters, and also have excellent RX/TX coverage where
it can hear those low powered trackers and other stations, and be
heard by them as well with minimal holes in the coverage.
I've argued this point for over a decade, and it falls of deaf ears.
We have built a digipeater network of over 30 digipeaters here in
Alberta, and they don't follow the intentional interference concept.
Our digipeaters wait for a clear channel. This means that packets take
slightly longer to propagate through the network (They are only 2 or 3
hops max), but the packets make it through the network reliably. We
also support the SSn-N concept, and have tested using AB7-7 numerous
times. I can reliably get 5 hops across the province. I can't get
further because 5 hops crosses the whole network!
- << Previous post in topic Next post in topic >>