Get your CTCSS tones right to access repeaters
One of the things that many newcomers to FM and repeater operation fail to do when programming a radio is to program the CTCSS tone properly. There’s even a question on the Technician Class exam that addresses this issue, question T2B04:
QUESTION: Which of the following could be the reason you are unable to access a repeater whose output you can hear?
ANSWER: All of these choices are correct
- Improper transceiver offset
- The repeater may require a proper CTCSS tone from your transceiver
- The repeater may require a proper DCS tone from your transceiver
But, what does this mean really?
CTCSS stands for continuous, tone-coded squelch system, and is a technique used to allow repeaters—and radios—to receive particular signals and reject others. The signals that a repeater (or radio) will receive are signals with a specific sub-audible tone, called a CTCSS tone, that has been added to the signal. So, even though your radio may be transmitting and receiving on the correct frequencies for a particular repeater, you won’t be able to access the repeater if you’re not also transmitting the CTCSS tone the repeater has been programmed to respond to.
There are 55 standard CTCSS tones:
Why do we use CTCSS tones? One of the reasons repeaters use CTCSS tones is that they often operate in environments where there is a lot of interference. On a tower or rooftop, for example, there may be several repeaters, a paging system, and other RF equipment. In such an environment, the generation of spurious signals could cause the repeater to think it’s receiving a signal on its input frequency and turn on its transmitter. If a sub-audible tone is required, however, the repeater will remain off until it hears a signal that was definitely meant to be repeated.
Another reason for using CTCSS tones is to prevent interference from other repeaters that use the same repeater frequency pair. Although care is often taken to minimize this interference, sometimes long-distance propagation can cause stations accessing a repeater to also access one many miles away. If the two repeaters use different CTCSS tones, however, this is not a possiblity.
How do you know what CTCSS tone you need to access a particular repeater? Well, one way to do this would be to check a repeater directory. If the repeater is operated by an amateur radio club, you could look up this information on the club’s website. Some repeaters will even announce the CTCSS tone that it requires. In most cases, the objective is to reduce interference and not restrict legitimate access.
So, if you’re not hitting a repeater when you think you should be, first check to see that you’re transmitting the correct CTCSS tone. Refer to your radio’s user manual for instructions on how to do this.
By the way, you may hear CTCSS tones sometimes called PL tones. PL is short for “private line,” and is what Motorola, the company that developed the CTCSS system called it. Since PL is a Motorola trademark, we now use the generic term CTCSS.