How about receiving APRS in flight?

[PaigeHoffart]

A post above suggested that monitoring all the local transmissions would be overwhelming, but effectively, you would only be aware of those stations that are transmitting on the area of the GPS map-screen you are currently viewing.

Just to clarify...Your receiver will be hearing everything within line of sight on 144.39. It doesn't matter what map you're looking at. If two stations transmit at the same time, the data packets will collide and both beacons will be lost. If there are 10 stations, no problem, if there are 200, we have a problem. Why would two stations transmit at the same time? Because they are probably at an elevation of 3' AGL and they can't hear each other. Unfortunately, if you're at 10,000' you're going to hear everything.

BTW, the other issue with hearing all of this congestion is that your tracker is waiting for a break in the action to transmit its packet. Imagine being in a crowded room, and you're unable to speak until everyone else is quiet.

Unfortunately, in some areas of the country APRS is a victim of its own popularity.

Here's one example of APRS congestion with only 50 stations:
http://mm.aprs.net/map.cgi?map=APRSw...call=*&range=1

For you guys in Fort Worth, I didn't bother counting:
http://www.findu.com/cgi-bin/map-near.cgi?zip=76137

Ok, enough with the doom and gloom. There are things that can be done to reduce the congestion.

1) Transmit less often (smart beaconing)
2) Reduce the number of digi's in your path (WIDE 1-1, 2-1, don't use RELAY)
3) Use a shorter beacon (mic-e compressed)

(Of course, this is a community effort)

How will it work in flight? Hard to tell.

Paige

[Davepar]

The Seattle area looks similarly crowded, but the timestamps indicate they aren't all transmitting right now. I took all the APRS stations near Seattle and put them into Excel and sorted by last update. Only 13 transmitted within the last 5 minutes. Doesn't sound like many collisions to me.

Isn't there something in the packet that indicates the vehicle type? We could filter on airborne vehicles.

I figured it was a long shot, but it sounds possible. I think many of the handheld GPS units can display traffic from a 327 transponder or other device. We should be able to fake that protocol pretty easily.

A side question on the WIDE 1-1, 2-1 path setting. Does that affect the ability for the packet to get onto the internet? I don't care how many digipeaters it goes through. I just want it to show up on a map on the web.

Dave

[PaigeHoffart]

Isn't there something in the packet that indicates the vehicle type? We could filter on airborne vehicles.

Yes, but collision wise it doesn't matter, the interference occurs at the RF level.

Only 13 transmitted within the last 5 minutes

That sounds very reasonable. Its been a few years since I lived in a congested area; maybe the new path types have paid off. With the old RELAY, WIDE, WIDE your beacon went out, and was immediately repeated by multiple digis. A receiver in the house would be receiving about 80% of the time. The other thing to note about the statistics off the web is that you will never see a collision, it will never be decoded.

A side question on the WIDE 1-1, 2-1 path setting. Does that affect the ability for the packet to get onto the internet?

The short answer is no, that is if the i-gate hears the signal directly. If the i-gate isn't within line of sight, then increasing the number of digis that it goes through gets you a better chance of eventually being seen by an i-gate.

Paige

[Sam Buchanan]

Originally Posted by PaigeHoffart

There are things that can be done to reduce the congestion.

1) Transmit less often (smart beaconing)
2) Reduce the number of digi's in your path (WIDE 1-1, 2-1, don't use RELAY)
3) Use a shorter beacon (mic-e compressed)

That is precisely the setup used in the default config of the Micro-Trak.

Originally Posted by Davepar

A side question on the WIDE 1-1, 2-1 path setting. Does that affect the ability for the packet to get onto the internet? I don't care how many digipeaters it goes through. I just want it to show up on a map on the web.

Dave

There is a great deal I don't know about packet protocol. This link will answer some of your questions and provide far more info than you probably wanted to know:

http://web.usna.navy.mil/~bruninga/aprs/fix14439.html

(By the way, Mr. Bruninga is the fellow who invented APRS)

Bottom line, we don't want to have more bounces in our beacon than absolutely necessary. The congestion problem increases exponentially when unneeded hops occur. The "WIDEn-N" protocol is designed to reduce congestion and seems to be providing good results for those of us using it.