On the interstates, we typically pass another ham about once every 20 minutes, yet may go for hours without finding a QSO on 146.52.

144.39 CTCSS 100 works far better than listening to 146.52, because on 52, someone has to be calling CQ every 2 minutes so that there is any chance of someone in range hearing them. Most dont, thus many QSO’s are lost.

Think of 144.39 as a RADAR ping. The vast majority of APRS mobile operators are pinging away once every minute or so with a PL 100 packet position report. This serves as an automatic “in-range” signal probe. But, not only are they transmitting with PL 100, they also have their speakers MUTED with CTCSS 100 so that they can then HEAR a voice call from ANYONE that calls them using PL 100.

Thus, if you hear a PL 100 signal on 144.39, you know the following:

1) He is in SIMPLEX range
2) He is LISTENING with his speaker for a voice call.

In APRS lingo, we call this “VOICE ALERT” since we are all driving around with one radio permanently on 144.39 anyway, we may as well use its speaker and “pings” on those rare occasions when someone wants to get our attention for voice by using PL 100.

CAUTION! WARNING!!!

1) VOICE ALERT is only for CALLING or ALERTING the other station by voice to QSY to your chosen voice frequency (usually 52)… Do not QSO on 144.39 or you are interferring with other traffic.

2) When you call someone on 144.39 PL 100, you MUST say “voice Alert” or he won’t know you are on 144.39. Voice Alert calls are rare, and without giving him a clue, he will assume your voice came on his other band… and he will answer you there, but you dont know what other band he is on, so you dont hear him and we have another “two-cars-passing-in-the-night”… with no communications established.

SO, Even if you never have used APRS, don’t overlook this simple “radar detector” for travelers in simplex range. It works. Maybe only a few times a day on a long trip, but it works better than waiting for someone
within 5 miles of you to call CQ on 52…

(This post was originally found at http://www.amsat.org/amsat/archive/amsat-bb/200312/msg00192.html)