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[aprssig] WRAP-UP MISSOULA MARATHON APRS SUPPORT

kc8sfq at mei.net kc8sfq at mei.net
Wed Jul 11 02:31:56 UTC 2012



Would time slotting the trackers help? I for one don't mind a special
event, and in fact, enjoy watching, even if I'm not participating. We have
one such event coming up on the 21st, but doubt we'll be using APRS. I'll
be loaning my tracker to our FIRST Robotics coach that week. He just
passed his Tech exam. Our students have seen my tracker and often track
me. Our coach is going to drive to Newington for the ARRL Teacher's
Institute and the students want to track him. those kids are SO much fun.
Bright inquiring minds.

73 de KC8SFQ
++++++++++++++++
> But I was not talking about overloading the channel for others.  I
was
> talking specifically about overloading a private event with
no other
> traffic, and colliding packets with your own
participants.  At 7 trackers
> and 30 second intervals, and 2
digipeaters, that is 42 packets per minute.
> With each packet
taking about a second, it is impossible for all of those
> packets
to be received reliably.
> 
> The casual observer will get
the feeling that everyone is getting fresh
> data, but it is the
collided packets from the weaker or more distant
> tracker
> that are not being heard reliably because most of its packets are
being
> clobbered by the closer trackers.  The "gaps" in
coverage may not be a
> range
> issue at all, its just
that those packets are weaker and are being
> clobbered
>
by stronger packets closer in.
> 
> The ALOHA channel has
been well  understood since the 60's when it has
> been
>
proven that any loading over 18% of channel busy only makes throughput
> worse.  Said another way, unless you hear nearly 80% quiet
between
> packets,
> then you can be assured that you are
not hearing everything, and that many
> of the packets are
suffering collisions.
> 
> For 7 trackers and 2
digipeaters, there is no way I would use 30 second
> reporting if
I wanted reliability.  Generally, I consider a channel (even
>
if
> it is private and exclusive) to not be able to support more
than 6
> one-minute trackers with only 1 hop.  12 trackers would
have to do 2
> minute
> rate to be reliable.  Adding two
hops will guarantee to make things worse.
> 
> Now of
course, IF your event used no digipeaters and all stations could
>
hear
> everyone else so that carrier detect could work, then you
could double
> these
> figures.
> 
>
Etc..
> 
> Bob, Wb4APR
> 
> -----Original
Message-----
>
From: aprssig-bounces at tapr.org
[mailto:aprssig-bounces at tapr.org] On Behalf
> Of Herb Gerhardt
> Sent: Tuesday, July 10, 2012 2:36 PM
> To: 'TAPR APRS
Mailing List'
> Subject: Re: [aprssig] WRAP-UP MISSOULA MARATHON
APRS SUPPORT
> 
> You folks must think outside the box. 
Every place is a unique location.
> Right now within 20 miles of
Missoula  there are a total of 8 APRS
> stations
> on my
map and only two digipeaters, so transmitting at 30 sec is fine and
> dandy FOR THIS LOCATION, it won't saturate the APRS network.
> 
> Our recommended path settings are for the entire US and
local paths which
> transmit more often are just fine in some
areas.  These areas not only
> have
> few users, they have
very few digipeaters or home stations that will digi
> the WIDE1-1
path, so only a few transmissions will hit a digi.  More often
>
might be better in some remote areas of our country.......
> 
> Also keep in mind that special events and Search and Rescue
missions have
> priority over normal local usage.  These are
usually of a short duration
> and
> for SAR, a life might
be at stake, so more often transmissions to make
> sure
>
you are being heard, are justified.
> 
> 
> Herb,
KB7UVC
> NW APRS Group, West Sound Coordinator
> Our WEB
Site:  http://www.nwaprs.info
> 
> 
> 
>> -----Original Message-----
>>
From:
aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On
>> Behalf
> Of
>> Brett Friermood
>>
Sent: Tuesday, July 10, 2012 10:01 AM
>> To: TAPR APRS Mailing
List
>> Subject: Re: [aprssig] WRAP-UP MISSOULA MARATHON APRS
SUPPORT
>>
>> > I count 7 trackers going at 30
second rate which is really pushing the
>> > Aloha limit on
a 1200 baud channel with digipeats. You may have lost a
>> >
lot of packets due to collisions...
>>
>> What was
the reasoning for 30 second transmit rates?
>>
>> At
a far off world record pace of 15 mph that is 1/4 mile traveled per
> minute, which
>> equates to the many times on this list
recommended minimum beacon rate.
> Ded
>> reckoning
will easily handle that even on an extremely curvy course.
>>
>>
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>>
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> 
>

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