APRS Digipeating and Path Selection 101

[cruiserlarry]

Larry,

For most systems it should stay at port 1. The field is there in case you are using a multiport system (more than one TNC or Frequency), it is also there to send a message via the APRS-IS internet system.

So again it should stay at port one for most applications. It has nothing to do with com port settings. I know that is confusing.

Hector

Confusing is an understatement; I set up the port in comm setup, and then it asks again in the messaging setup - I figured the comm setup was port 1 as we discussed, and that the messaging port was the comm port my laptop used to communicate with the TNC (WRONG !!!)....Maybe that is my issue with the messaging feature - I'll set it to port 1, and try it this week...

[hmfigueroa]

Now for another wrench, what do you recommend for power levels? I try to stick with 10W, but some of the self-contained trackers and of course the APRS HTs are only 5W or less. Are my chances of hitting an Igate any better by bumping the power from 10W to say 20W?

In order to comply with FCC regulations and be a good neighbor for HT and low power tracker users, You should not use more than 10 watts. The problem is that most HTs are limited to 5 watts max, and if you use more than 10 watts you are more likely to hit multiple high digipeaters and cause interference to yourself. This is not to say you cannot run more power, you can, if it is necessary.

Ideally you want to only hit one high level digi at a time, then have that digi digipeat to another digipeater and have that digipeat to an i-gate station. This is true for most Southern California Stations. The average route to a full time igate in this area is two hops. This may not be true for other areas of the country.

[sdnative]

The Unproto path is correct on UI View 32...next idea

Is there a NOGATE setting on your radio? May want to make sure that is turned off.

[DaveK]

In order to comply with FCC regulations and be a good neighbor for HT and low power tracker users, You should not use more than 10 watts. The problem is that most HTs are limited to 5 watts max, and if you use more than 10 watts you are more likely to hit multiple high digipeaters and cause interference to yourself. This is not to say you cannot run more power, you can, if it is necessary.

Hector, your 10 watt recommendation seems to be at odds with Stephen Smith's article, above. Smith states:

Signal levels that you may consider adequate on voice WON'T BE on packet, because data transmission is an all-or-nothing proposition. --ALL-- of a packet has to be received PERFECTLY to recover --ANY-- data from it. The kind of noisy, scratchy, not-completely-hard-quieted, operation so many people inflict on voice repeaters with underpowered handhelds, JUST WONT WORK on data transmissions. A pop, a momentary burst of white noise, flutter, or multipath-induced phase distortion that you don't even notice on voice WILL be fatal to a packet transmission.

Signals to/from mobile units can and do fluctuate in strength by 15-20 dB as the mobile moves over even a short distance. For reliable data transmission, you must have massively excess signal strength over the intended path. Enough excess signal that even with a 20dB drop, the signal will remain noiseless and hard quieted. [ Note that the instruction manual for the Kenwood D700 acknowledges this fact by stating that you can't expect reliable packet operation until the S-meter reads full scale.

Roughly speaking, a given antenna installation and transmitter power will produce about 1/2 to 1/3 the RELIABLE range on APRS packet that it produces on FM voice.

10 watts does not seem like "massively excess signal strength" when you consider that (according to Smith) you will have a 1/3 to 1/2 reduction in reliable range.

[hmfigueroa]

Roughly speaking, a given antenna installation and transmitter power will produce about 1/2 to 1/3 the RELIABLE range on APRS packet that it produces on FM voice.

10 watts does not seem like "massively excess signal strength" when you consider that (according to Smith) you will have a 1/3 to 1/2 reduction in reliable range.

You should always use the minimum power necessary to complete the commuications. To use 50 watts when it isnt needed is not a good general practice. It is far better to have an efficent antenna system and lower power, that way you have a reserve of power to use when you absoultely need to get out. Using a lot of power will exclude the low power users, like a search and rescue user using a portable tracker or HT.

I don't know the context of Steve's article, but I think it speaks to the need to have a good clean signal,(proper audio levels, equalization, twist, and frequency) in order to be properly decoded. This would be more useful in traditional mode packet radio where your are transfering data, it is far less important in unconnected modes like APRS.

I was running 10 watts on our Parashant Trip because that was the minimum my radio will put out. I did not do a specific comparison of our tracks, but as I recall they were similar. Were you using more than 10 watts?

APRS data is meant to be timely with old data being less and less useful. It is meant to be the latest position, stuff like messages have automatic retries if they are not acknowledged to improve the chances of making it through pitfalls of the RF environment.

[DaveK]

Roughly speaking, a given antenna installation and transmitter power will produce about 1/2 to 1/3 the RELIABLE range on APRS packet that it produces on FM voice.

10 watts does not seem like "massively excess signal strength" when you consider that (according to Smith) you will have a 1/3 to 1/2 reduction in reliable range.

You should always use the minimum power necessary to complete the commuications. To use 50 watts when it isnt needed is not a good general practice. It is far better to have an efficent antenna system and lower power, that way you have a reserve of power to use when you absoultely need to get out. Using a lot of power will exclude the low power users, like a search and rescue user using a portable tracker or HT.

I don't know the context of Steve's article, but I think it speaks to the need to have a good clean signal,(proper audio levels, equalization, twist, and frequency) in order to be properly decoded. This would be more useful in traditional mode packet radio where your are transfering data, it is far less important in unconnected modes like APRS.

I was running 10 watts on our Parashant Trip because that was the minimum my radio will put out. I did not do a specific comparison of our tracks, but as I recall they were similar. Were you using more than 10 watts?

APRS data is meant to be timely with old data being less and less useful. It is meant to be the latest position, stuff like messages have automatic retries if they are not acknowledged to improve the chances of making it through pitfalls of the RF environment.

Hector:

Thanks. I still feel like I am in the dark on this subject. I know that we are all told not to use more power than is needed, but I neither know of a way to determine how much power to use while mobile or any reference material which can guide me. In the area of voice communication, the need for more power is immediately evident and the benefit can be seen as quickly. In the area of APRS, it would seem that the only way to determine how much power would be necessary would be to run the same course at least a couple of times with different power settings and then compare the results - rather time consuming. While this might prove useful, what happens when your next trip takes a different route or is to a different place? What if part of your trip requires more power and part of your trip requires less?

Smith talks about "underpowered handhelds", a 1/3 to 1/2 reduction in reliable range and a 20dB drop in signal while mobile, and I cannot help but think that max power is indicated (50W in my case).

I also looked at the difference between Ollie's and Eric's results from their recent trip and I, again, cannot help but conclude that power was the difference.

As an FYI, I ran 50W in the Parashant.

[OLLIE]

It should be interesting to see how my HT with external antenna at 5W holds out on my trips to Mexicali in the next few days.