What are CTCSS and DCS

If you are programming repeaters into your radio or working certain satellites, you likely encountered the above. This is not a full background or technical paper on either CTCSS or CDS but it has enough to get you to understand them and get going.

Let's start with CTCSS which stands for Continuous Tone Coded Squelch System and is used in the "Analog" repeater world at times to squelch unwanted traffic. This signal, while technically audible, is below the normal analog speech as is generally received by radios. It is often called sub-audible, but this is not technically correct. If you were to listen with full spectrum or low frequency capable speakers, such as a sub-woofer, you would be able to hear it unless you radio pre-filters it. Many do this already as do many repeaters before re sending the signal. In the repeaters case, it is sometimes done for added security. Generally this will be a  tone between 67 and 254.1Hz. Generally speaking, CTCSS is a little more forgiving then DCS and has much wider implementation as well as compatible with older radios.

Was originally developed by Motorola, who of course, is known for massive contributions to radio technology over the years. Below is a list of commonly used CTCSS as well as the corresponding Motorola Equivalents used in some (mu understanding is, mainly older) systems.