What is a CTCSS or Tone filter?

What is  CTCSS or Tone?

Modern radios can not only hear a transmission on a specific frequency but also apply a filter. This filter is implemented by sending a CTCSS tone. These tones are often referred to as sub-audioable as they are outside the range of what we can hear.

When set to a receiver, it will only allow you to hear audio from the specific FHZ set that contains the correct CTCSS tone. So what they do is act as a filter on the channel. While your radio may hear other transmissions or noise on the channel, if they do not contain the correct tone, they will NOT be heard by the radio user.

What are the dangers of using CTCSS tones?

While they sound like the answer to many problems, they only work when transmitters are configured to send them. Our experience has seen that, while they are mandated, not all tracks have them set to be sent. If your receiver is configured to hear only tone-encoded transmissions and the event organisers have radios that are not set to send tone, you will NOT hear their transmissions.

What happens if my Receiver does NOT have a CTCSS tone set?

Nothing, what this means is that you will hear all transmissions on the channel. It will not in any way affect your ability to hear race control. The downside of not having the tones configured is that, because your radio will hear everything on the set channel, you may be susceptible to noise or interference.