N8DEU_APRS-basics

A discussion on APRS basics,
from an exchange on the 'HARC-AL' YahooGroup email reflector - June 2008

- this exchange was prompted by Tim's article in the HARC-VOX newsletter for July 2008
"APRS - The Tactical Communications Solution for the Emergency Network"
-Travis (KE3Y) was asking Tim (N8DEU) for some basic setup info
- both have graciously allowed SomeNet to re-publish their dialog
(this is part < 1 - 2 - 3 > of a special series)

----- Original Message -----
From: "Tim Cunningham" < n8deu@_x_x_x_>
To: "Travis" < ke3y@_x_x_x_>
Cc: < harc-al@yahoogroups.com >
Sent: Monday, June 23, 2008 10:56 AM
Subject: Re: APRS basics

Hi Travis,

> I read your passionate article in the VOX about APRS for emergency nets.

You could say I am a little a passionate about my hobby.
Anything worth doing is worth doing it well.

> Could you say what minimum and recommended equipment is needed to transmit APRS text for each of two situations: Fixed station with Internet access; and a mobile station.

The beauty of the APRS tactical communication system is the lower cost entry point in comparison to some of the other digital modes. They all have their unique usefulness in different ways.

For a fixed station the following equipment scenario's could be utilized for messaging.

1. Radio, computer, and use the sound card with AGWP software as the TNC.

2. Radio, computer, and TNC. A TNC could be a standard 1200 baud AX.25 Kantronics, MFJ, Pac-Comm, Symtek or it could be a TNC-X (KISS only TNC).

3. Computer with Internet access (no radio or antenna required). APRS works seamlessly between the RF world and the Internet. I once had a keyboard QSO with a German HAM via my 2 meter APRS mobile driving through the hills of WV and found that he had been tracking my travels the entire day.

4. Kenwood TMD-700A or TMD-710A mobile. Kendwood TH-D7A handheld. They have a built-in 1200/9600 baud TNC and an interface on the display where you can send messages back and forth without a computer by using the buttons on the microphone to compose messages. I just had a QSO with a HAM in Decatur from my mobile this morning driving down I-65. The Alinco DR-135T has a built-in 1200 baud TNC to support APRS as a tracker but it does require a computer for messaging or you could use a Palm Pilot or any Windows CE or Windows Mobile handheld device. They all have the ability to act as digipeaters to help move traffic from one location to another if line of site is an issue or a digipeater goes down (no proprietary software required). Every station on the network can be utilized as a digipeater if needed. This adds some redundancy to the network. My cell phone by itself works great in a handheld application since it also has a buit-in GPS and eliminates the need for a laptop.

A mobile station with messaging capability can consist of the following configurations:

1. Radio, TNC, and a laptop computer or Palm Pilot or Windows CE or Windows Mobile handheld device. A GPS is optional unless you want/need to provide real time location information. Some users opt to forego the GPS and manually indicate their position by clicking it on a map. Objects can be placed on a map by any user to alert others of pertinent activity or issue at that location (power lines down, traffic blocked, tornado damage, etc). NWS mesages are also received by all stations in a simultaneous broadcast protocol in the event of severe weather. APRS users always know what is happening with the weather instantly.

2. Radio, laptop, and use the sound card with AGWP software as the TNC.

3. Kenwood TMD-700A or TMD-710A. It has a buit-in 1200/9600 baud TNC and an interface on the display where you can send messages back and forth without a computer by using the buttons on the microphone to compose messages. One of the Alinco Radio's have a built-in 1200 baud TNC to support APRS as a tracker but it does require a computer for messaging or you could use a Palm Pilot or any Windows CE or Windows Mobile handheld device. My cell phone works great in this application since it also has a buit-in GPS and eliminates the need for a laptop or a desktop as it performs that function. Heck, my phone eliminates the need for a radio since it has internet access, APRS software, and a built-in GPS.

4. There are numerous other configurations with tracker only capability, etc...

> For those 2 categories, what software and firmware is needed, and what operating systems are supported?

Basically, most operating systems are supported like Linux, DOS, Windows, MacIntosh, Palm Pilot, Window Mobile, Windows CE, etc... The Kenwood radios can be used as a standalone system since they have a user interface. Although, you could connect a computer to the Kenwood radio and use it as well.

APRS software is generally required on a computer along with a map application (Delorme Street Atlas v9.0 or lower and not the Deluxe version, Precision Mapping, Microsoft Mapping, and many support screen capturing of a map to utilize. The screen capture method provides the ability for everybody to view the same map display, but it does not allow you to zoom into street level detail like the software map programs.

> What equipment and software would be needed by a net control station to see the weather bulletins, the map plot, and a list of all the check-ins--and respond by radio?

A 2M Radio, computer, and a TNC unless you use a radio with a built-in TNC or use the sound card as the TNC. You would also need one of the many APRS software packages. Some are free and some require a registration fee. The final piece would be the mapping software which can be Delorme Street Atlas verion 9 or below, Precision Mapping software, Microsoft Maps, or captured maps from a screen shot. The weather bulletins are transmitted in real time from the local I-Gate immediately. You could get by without a radio if you had an Internet connection. In real disaster, we would rely on the radio network link and battery back-up power.

> How would an APRS-centric weather net operate?

Not much different than the voice net. A message can be broadcast to all users opening the net and inviting check-ins by indicating what they should provide in their response. When the message is received by the net control the users software will get an acknowlegment message that their message was received so their transmiter will not repeat the traffic and free up the data channel. The net control can have an automatic message returned to the sender immediately upon receipt with an automatic message to their inbox or the net control can chose to manually acknowledge with individual messages or a broadcast to all stations with a list of those stations that are being acknowledged (the best approach to reduce data congestion).

> What is the max. size of any one text or weather message, not counting the usual position information? (Would stations give detailed reports via voice?)

There is really no maximum size of a message with the exception of how much data is sent in a single packet. A paragraph of text can be sent at one time, although it will be broken down into multiple transmission of data as to prevent hogging the bandwidth of the data channel. APRS is designed to process the most current information as quickly as possible. The Kenwood data radios may limit a line of text to 40-60 characters on a single line. Some of the software packages also limit data to 60 characters per line, but they are simply sent in an additional transmission as a separate message and in the logical order so it can be read as intended. Bulletins broadcast to all stations are very easy to ready when multiple lines of text are transmitted.

> A basic and elementary answer (or column) from you would be appreciated, though I imagine you also know some Web sites to refer us to.

Here is some good information to read:
http://www.n5oom.org/2004_hamcom/presentations.htm

> Also you might want to reply on harc-al@yahoogroups.com to get 30 or 40 readers.
> Thanks,
> Travis Hardin, KE3Y

Have a Great Day!
Tim- N8DEU