The club has adopted channel 20 for normal operations. Again, this can be on an FRS or a GMRS radio. On this channel, FRS radios may use 2 watts of power, but GMRS radios may use up to 50 watts.
But there is an additional twist. We say the club uses channel 20/20. The second 20 in 20/20 is what is called the CTCSS code and it is set separately from the channel.
Both FRS and GMRS use a CTCSS system intended to reduce conflict between users on the same channel. It stands for Continuous Tone Coded Squelch System. That is a mouthful, but it is actually a pretty simple idea. Each radio can select a CTCSS frequency to transmit and listen for. They are low-pitched audio tones that you can’t hear but the radio can. Your radio will reject, i.e. squelch, signals that don’t include the correct tone in the background. Two radios using the same tone will hear one another but will ignore radios using a different tone.
CTCSS codes are sometimes called sub-channels or privacy codes, but they don’t really provide privacy. If you set your radio to no CTCSS code you will hear all transmissions on the channel regardless of their CTCSS tone.