Van's Air Force
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APRS Congestion
- Thread starter Ron Lee
- Start date
Congestion on APRS
Ron,
The APRS system can handle a tremendous number of users if used wisely. Even in areas with very high user density, the system is still very effective. Remember though, that this is ham radio, and there are no guarantees that the service will not be overwhelmed. Digipeater owners can provide a list of "authorized" callsigns to their machines, locking out others (us) from access.
The bright side is that the system is virtually unlimited from the Internet side of things, so adding additional channels (operating frequencies) can double the capabilities of an area overnight. There are areas of the country where the primary APRS frequency is augmented by a seperate frequency.
I encourage people to use the MIC-E compression format. Although it has the downside of removing a little accuracy from your position report, its shorter packets are much more likely to be heard by a digipeater, and processed without corruption. This is similar to the way we can hear the person across the table say "yes" or "no" in a noisy room, when anything beyond that is lost in the noise layer.
I advocate the use of APRS because unlike other "tracking" systems, the APRS system provides an archive of your last known position. ELT's, Satellite based locators, etc. for the most part are either manually activated, G-activated, or remotely interrogated, and don't work if you don't, won't or can't , push the button. APRS will give us SAR people a clue where to start looking if there is a problem. Let me climb down off my soap box now....
Allen
VHS
www.byonics.com/microtrak
Ron,
The APRS system can handle a tremendous number of users if used wisely. Even in areas with very high user density, the system is still very effective. Remember though, that this is ham radio, and there are no guarantees that the service will not be overwhelmed. Digipeater owners can provide a list of "authorized" callsigns to their machines, locking out others (us) from access.
The bright side is that the system is virtually unlimited from the Internet side of things, so adding additional channels (operating frequencies) can double the capabilities of an area overnight. There are areas of the country where the primary APRS frequency is augmented by a seperate frequency.
I encourage people to use the MIC-E compression format. Although it has the downside of removing a little accuracy from your position report, its shorter packets are much more likely to be heard by a digipeater, and processed without corruption. This is similar to the way we can hear the person across the table say "yes" or "no" in a noisy room, when anything beyond that is lost in the noise layer.
I advocate the use of APRS because unlike other "tracking" systems, the APRS system provides an archive of your last known position. ELT's, Satellite based locators, etc. for the most part are either manually activated, G-activated, or remotely interrogated, and don't work if you don't, won't or can't , push the button. APRS will give us SAR people a clue where to start looking if there is a problem. Let me climb down off my soap box now....
Allen
VHS
www.byonics.com/microtrak
Noah
Well Known Member
Allen, Please tell us more about how Mic-E compression works.
"What happens IF APRS became the predominant tracking system for GA?"
I don't think your average spam-can driver is willing to spend the time to get a ham license (or get a field approval for a dedicated APRS tracker). RV builders, being true experimentalists and DIY types, are a different breed.
Its ground-based hams that are the real concern, and people should give some serious thought to whether they really need to blast a signal out at 8 watts if 3/10 watt gets you what you need. That will do a lot to ease congestion, given the heights our aircraft fly and the number of digipeaters available line of site from that altitude.
"What happens IF APRS became the predominant tracking system for GA?"
I don't think your average spam-can driver is willing to spend the time to get a ham license (or get a field approval for a dedicated APRS tracker). RV builders, being true experimentalists and DIY types, are a different breed.
Its ground-based hams that are the real concern, and people should give some serious thought to whether they really need to blast a signal out at 8 watts if 3/10 watt gets you what you need. That will do a lot to ease congestion, given the heights our aircraft fly and the number of digipeaters available line of site from that altitude.
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kevinh
Well Known Member
I don't think your average spam-can driver is willing to spend the time to get a ham license (or get a field approval for a dedicated APRS tracker). RV builders, being true experimentalists and DIY types, are a different breed.
Three more ideas:
1) We should do some experiments with the SmartBeaconing to find the minimum transmit rate that still gives accurate positions for our fast moving beasts.
2) We also might want to include our email addresses in our status message to make it easy for other hams to tell us if we've violated some local mores before we annoy anyone too much.
3) To keep my transmissions short, I've set my microtrak to only broadcast my status message every eight transmissions - because I should be sending out position updates pretty frequently anyway.
(I've received my microtrak and I have it all ready to go except for the GPS - I can't wait to start playing around)
PaigeHoffart
Well Known Member
Quoting Sam Buchanan:
Sam,
I am optimistic that aprs congestion may be much less of an issue than it was a few years ago. My concern though was mainly with receiving aprs airborne, or with trackers that waited for a clear channel before transmitting. I believe the units you are using don't have a receiver, and will just step on any other transmissions (one reason to use low power, a long beacon interval and smart beaconing). Quoting the Micro-Trak 300 manual "The combination of the Micro-Trak 300 and the TinyTrak 3 PIC produces a hybrid that is capable of being adapted to virtually any portable APRS project. It is important to remember, that this is a transmit-only system, and may transmit coincidentally with other APRS transmitters"
If you and a mobile ground station transmit at the same time, the ground stations that can hear both of you will probably get nothing (although if one of you is running considerably higher power, the FM capture effect may let that packet get through). The ground station that can only hear you will still repeat your packet to the igate, so you won't notice the fact that you stepped on someone else.
I'd like to see what happens with an airborne receiver.
Paige
Sam,
I am optimistic that aprs congestion may be much less of an issue than it was a few years ago. My concern though was mainly with receiving aprs airborne, or with trackers that waited for a clear channel before transmitting. I believe the units you are using don't have a receiver, and will just step on any other transmissions (one reason to use low power, a long beacon interval and smart beaconing). Quoting the Micro-Trak 300 manual "The combination of the Micro-Trak 300 and the TinyTrak 3 PIC produces a hybrid that is capable of being adapted to virtually any portable APRS project. It is important to remember, that this is a transmit-only system, and may transmit coincidentally with other APRS transmitters"
If you and a mobile ground station transmit at the same time, the ground stations that can hear both of you will probably get nothing (although if one of you is running considerably higher power, the FM capture effect may let that packet get through). The ground station that can only hear you will still repeat your packet to the igate, so you won't notice the fact that you stepped on someone else.
I'd like to see what happens with an airborne receiver.
Paige
Paige,
You are correct that the Micro-Trak is a transmit only device. Sending packets blindly has always been a contraversial proposition. When I introduced an 8 Watt version, there were howls of outrage from hams bemoaning the swamping of the network. So far, the world has not come to an end. The idea of sending coordinated packets, by "agreeing" with a digipeater and "scheduling " a transmisison has arisen in the past. Like Cellular phone, the idea was to make a truly coordinated system. I don't think that's ever going to happen.
Obtaining throughput with APRS is accomplished by achieving FM capture with a digipeater or I-Gate ( I Know you know this, you impressed the heck out of me with your other posts!) We are competing with mobile stations that may be transmitting hundreds of Watts. Like talking to my wife, the key is to be brief, poignant, and speak at the precise time with words that will have the most effect.
APRS transceivers based on the TinyTrak or Open Trac or similar encoder monitor the frequency for noise, and hold off transmitting until a quiet time before releasing the transmitter to send a packet. Unfortunately, if every transceiver plays the same game, everyone on the palying field ( of equal power and receive capability) will send their signals more or less coincidentally. The best signal to a single I-Gate or digipeater may cause the machine to assume FM capture and win the game of king-of-the signals.
All APRS packets are effectively sent randomly. The effect of using an Airborne receiver to hold off transmissions would be to keep the aircraft from transmitting forever. The aircraft would have +9 reception of signals from hundreds of miles away. The best strategy is to send your data, hope that your tiny little signal can find its way into a system, and use good and best practices to avoid overwhelming the network.
Allen
VHS
You are correct that the Micro-Trak is a transmit only device. Sending packets blindly has always been a contraversial proposition. When I introduced an 8 Watt version, there were howls of outrage from hams bemoaning the swamping of the network. So far, the world has not come to an end. The idea of sending coordinated packets, by "agreeing" with a digipeater and "scheduling " a transmisison has arisen in the past. Like Cellular phone, the idea was to make a truly coordinated system. I don't think that's ever going to happen.
Obtaining throughput with APRS is accomplished by achieving FM capture with a digipeater or I-Gate ( I Know you know this, you impressed the heck out of me with your other posts!) We are competing with mobile stations that may be transmitting hundreds of Watts. Like talking to my wife, the key is to be brief, poignant, and speak at the precise time with words that will have the most effect.
APRS transceivers based on the TinyTrak or Open Trac or similar encoder monitor the frequency for noise, and hold off transmitting until a quiet time before releasing the transmitter to send a packet. Unfortunately, if every transceiver plays the same game, everyone on the palying field ( of equal power and receive capability) will send their signals more or less coincidentally. The best signal to a single I-Gate or digipeater may cause the machine to assume FM capture and win the game of king-of-the signals.
All APRS packets are effectively sent randomly. The effect of using an Airborne receiver to hold off transmissions would be to keep the aircraft from transmitting forever. The aircraft would have +9 reception of signals from hundreds of miles away. The best strategy is to send your data, hope that your tiny little signal can find its way into a system, and use good and best practices to avoid overwhelming the network.
Allen
VHS
