What is APRS Voice Alert ?

APRS Voice Alert

Ever got frustrated of not being able to contact a passing by station you just saw on APRS? APRS can also work as a nearby station radar and help you out with that.

While driving on highway you are not always starring at the radios display and maybe you could miss a nearby station passing by or even on parallel road.

How do I use voice alert ?

It simply works by setting a tone on both transmit and receive on your APRS radio.

The following tones are used depending on your region.

  • USA: CTCSS 100
  • Europe: CTCSS 136.5
  • Australia: CTCSS 91.5

Once an APRS frame with a matching tone is received you’ll hear the sound of the APRS data in your speaker. Now you have several options :

  1. Look at your display and maybe the station you just heard is sending out frequency information, you could just try to QSY to that frequency and give a shout.
  2. Switch to you APRS radio/VFO and make a short voice call on the APRS frequency using the same tone as for voice alert. Since the other station is also using the same tones the operator will hear your voice through his APRS radio. Keep the call short an immediately propose a QSY !

Off course you can try one or both solutions.

How does it work ?

Since only mobile stations or attended stations (see Voice alert etiquette below) shall be using voice alert you will only hear stations which are in direct range. When you receive an APRS frame via a digipeater it will not be transmitted with the matching tone and therefore your speaker will remain quiet but the frame will still be decoded.

Voice alert etiquette

To avoid annoyance to other stations the following rules should be followed to the letter.

  • Only for attended operations!
    Voice alert should only be used if you are sitting behind the radio i.e. Imagine how upsetting it can be if someone is hearing your APRS beacon and is unable to make contact.
  • Immediat QSY !
    Whenever you make a voice call on the APRS frequency, keep it short a QSY ASAP ! Do not block the APRS channel !

Voice alert implementation

Commercial Radios

As far as I know following radios support voice alert. If I am missing one just let me know.

  • Kenwood TH-D72
  • Kenwood TH-D74
  • Kenwood TM-D710
  • Kenwood TM-D710-G
  • Yaesu FTM-350 (With latest firmware)
  • Yaesu FTM-400

Home made APRS setups

If you are using a tracker or TNC it is most likely that you are getting the receive signal out of the radio’s speaker jack. The issue is that whenever you enable a tone the speaker will be quiet unless the radio receives a signal with a matching tone. As a matter of fact your tracker will only be able to decode signal with voice alert.

To overcome the latter issue the receive signal must be tapped in the receiver chain before tone muting is applied to the audio signal. This is what I did with my Retevis RT98.


Voice alert is another nifty tool on the APRS Swiss Army knife. It will help you get in touch with hams in your vincinity easily. Keep in mind to use it attended only so that every one can have fun out of it !

Source : http://www.aprs.org/VoiceAlert3.html

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