[aprssig] Yet Another Clueless Balloon Launch

Bob Burns W9BU w9bu_lists at rlburns.net
Fri Jun 27 18:36:24 CDT 2014


On 6/27/2014 5:07 PM, Mike Goldweber wrote:
> Perhaps in a future version of the standard a simpler way can be found
> to set up the controls for how data is propagated?

Maybe I've been around it too long, but the concepts seem very simple to me.

1. If you don't need support from fill-in digipeaters, use WIDE2-1 or 
WIDE2-2. This is generally true of stations in fixed locations.

2. If you want support from fill-in digipeaters, use WIDE1-1,WIDE2-1 or 
WIDE1-1,WIDE2-2. This is generally true of mobile APRS users.

3 In all cases, adding up the numbers after the hyphens is the number of 
hops you are asking for. WIDE2-1 is one hop. WIDE2-2 is two hops. 
WIDE1-1,WIDE2-1 is two hops. WIDE1-1,WIDE2-2 is three hops.

4 In all cases, asking for more hops increases the chances of your 
packet being acted on by more digipeaters than the number of hops you 
ask for because your packet won't be digipeated in a straight line. 
Stephen Smith WA9LMF, the guy who started this thread, has a wonderful 
animated .GIF on his web site that demonstrates how digipeater hops work.

http://wa8lmf.net/DigiPaths/NNNN-Digi-Demo.htm

The general problem that Stephen is complaining about is APRS users 
asking for more hops than necessary.

Let's say you are a mobile APRS user running about 10 watts into a 
quarter-wave antenna that's about 5 feet off the ground. Depending on 
where you are, your initial packet may be heard by one, two, maybe three 
digipeaters. If your hop request is reasonable, let's say 
WIDE1-1,WIDE2-1, the number of digipeaters that will be triggered by 
your packet will be manageable. Depending on the local APRS 
infrastructure, your packet may be digipeated out 50 or 100 miles.

On the other hand, let's say you are a high-altitude balloon beaconing 
away at 50,000 feet using WIDE1-1,WIDE2-2. Because your antenna is at 
such a high elevation, a lot more digipeaters are going to hear you. A 
lot more. Digipeaters over a radius of hundreds of miles are going to 
hear your initial packet. And, because you asked for three hops, all 
those digipeaters are going to digi your packet out to hundreds more 
digipeaters.

To make this situation worse, let's say you are beaconing every 30 
seconds. The result is APRS chaos over a very wide area.

At the root of this problem is the fact that many APRS users have no 
idea how the APRS infrastructure works or their impact on that network. 
Sure, the balloon Stephen complained about may be getting great position 
data into the network. But, they are dominating the frequency to the 
detriment of other users.

Bob...


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