[aprssig] PL 100 on a base station

Bob Bruninga bruninga at usna.edu
Mon Apr 23 08:51:27 CDT 2007

> I need more info.  Is voice being used on the 
> APRS channel for long chats?  Is data being 
> heard on a voice channel?   

Neither.  VOice Alert is a recognition that all APRS mobiles have a dedicated receiver on 144.39.  This means that if you have no other way of konwing what frequency someone is monitoring, that you can always call him on 144.39 if he has the volume turned up.

The way to indicate to others that you are listening on 144.39 is to be running CTCSS 100.  This marks your packets with a PL of 100 so that others can tell you are listening.

As a side light, if they have CTCSS 100 set, then they dont have to hear anything on channel except such a packet from another Voice Alert station who comes within about 3 to 5 miles.  THink of it as a built-in proximity radar.

But the WORST THING EVER is for someone to be transmitting PL 100 and NOT BE LISTENING.  This is very frustrating to mobiles who may not hear a nearby voice-alert traveler for days or weeks, so it is exciting when he actually passes within simplex range of someone else.  

But if EVERY DAY, ALL DAY LONG, EVERYWHERE in his town, he hears a PL 100 station because it is a base station and NO ONE IS THERE LISTENING, then it is very frustrating and kills the utility of the system.

The purpose of Voice Alert is to be aware of being in simplex range of another APRS voice-alert station, and if you want to chat, to call each other and QSY for the chat.

See the web page:


Hope that helps.

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