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   Home   Help Search  
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Author Topic: New to APRS, need help.  (Read 2290 times)

Posts: 100

« on: May 05, 2006, 09:53:21 AM »

Good morning,
I have been licensed as a tech for about a month and own an Icom 208H that I use mobile.  When I bought it, i never thought I would have a need to use APRS.
Enter SKYWARN Spotter participation!
I am now a storm spotter and make my reports while mobile.  After making a few reports, I began wondring about APRS for reporting my position.  I have done a little reading on equipment and have determined that my radio has a packet ineterface.  I have looked at a few GPS receivers and the TinyTrak line, and figure that I can find a setup that will work.
However, my question is...
How does APRS work?
I understand (at least I think I do) that the GPS sends data to the TinyTrak.  The TinyTrak modulates it, and the radio takes that data and transmits it.
However, what happens when I make a voice report on the weather?  Does my position (data) get transmitted along with my voice report?
Do I need to transmit the APRS data on one frequency, and voice reports on another?
I am totally confused, but want to know how I can make a mobile system work.  It would let me focus on giving weather reports and not have to worry about where I am (especially if I am in an unfamiliar location) as well as automatically reporting my position to the NWS, saving them the trouble of having to manually plot where I am.

Any help is appreciated!



Posts: 99

« Reply #1 on: May 05, 2006, 06:21:44 PM »

If your APRS beacon is hoooked to your radio it'll probably be dedicated on the APRS freq 144.39.  If you want to Xmit and receive voice on another freq you will most likely need another radio.  
I get around this problem using a Kenwood TM-D700 dual band mobile.  One side of the radio is dedicated to monitoring and Xmiting on APRS.  The other side, B side, is used for 2m and 440 repeaters. The GPS data goes to the radio which has a built in TNC. My position and status data is beaconed at programmed intervals. The radio can be used as a APRS receiver and transmitter just fine by itself but I added a Laptop running Ui-View tracking software.  Great program which allows me to see my location and the location of other APRS stations on maps that can be zoomed down to street level.  
APRS would be a great source of info for anyone involved in SKYWARN.  Your net control will be able to monitor spotters locations and always know your position relative to storms.

Posts: 14491

« Reply #2 on: May 05, 2006, 06:23:46 PM »

You are correct that the GPS receiver sends its position to the TNC which then creates the data packet and modulates the transmitter with AFSK tones. Normally the TNC keys the transmitter and sends the position packet at some preset interval (every 10 minutes for example) on a dedicated APRS frequency.

Some commercial systems "burst" out a position packet at the beginning (or end) of each voice transmission on the voice frequency. I don't know if any ham networks are doing that or not. Of course it requires that the receiving stations be equipped to decode the information and display it on a computer map.

You really need to check with the people on the storm spotter network that you are working with to see what capabilities they have.

If you can't do it automatically then just carry a GPS receiver and give your lat/long position via voice.

Bob  AA4PB
Garrisonville, VA

Posts: 884

« Reply #3 on: May 12, 2006, 08:06:09 PM »

aa4pb wrote: "Some commercial systems "burst" out a position packet at the beginning (or end) of each voice transmission on the voice frequency"

This is refered to in the aprs protocol as Mic-E mode. The idea is that you key up the mic and your position is transmitted before you are able to speak (or maybe that's the other way around). If you are running through a repeater the packet will be sent quickly enough to be unlikely to go through the repeater. However, I don't know that it is in use, and you may have problems if you are some distance from the other stations you are communicating with (very true if going through a repeater).

The benefit of the APRS network is the network itself. Since most of the fixed stations in homes are connected to the APRS-IS servers, it becomes very easy to connect to a digipeater and ultimately allowing net control to be anywhere within a voice connection. When running MIC-E, you loose the APRS network, unless you configure some sort of digi-gateway.

At any rate, APRS would be a great aid in stormchasing, especally when used with a weatherstation. The messaging services could also be very useful for reporting funnel clouds and other data, along with group messages (one very under-utilized feature of APRS, in my opinion) and other stuff.
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