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.

CTCSSMotorola
67XZ
69.4WZ
71.9XA
74.4WA
77XB
79.7WB
82.5YZ
85.4YA
88.5YB
91.5ZZ
94.8ZA
97.4ZB
1001Z
103.51A
107.21B
110.92Z
114.82A
118.82B
1233Z
127.33A
131.83B
136.54Z
141.34A
146.24B
150none
151.45Z
156.75A
159.8none
162.25B
165.5none
167.96Z
171.3none
173.86A
177.3none
179.96B
183.5none
186.27Z
189.9none
192.87A
196.6none
199.5none
203.5M1
206.58Z
210.7M2
218.1M3
225.7M4
229.19Z
233.6none
241.8none
250.3none
254.10Z

Please note: There are some ADDITIONAL codes used, but mainly by some specific manufacturers such as Kenwood and are cleanly not cross compatible. Avoid using these if possible unless you have a specific reason to.

DCS stands for Digital Coded Squelch and is what you will encounter in the "digital" world...sort of. It is a digital signal being sent along side the audio (which can be Analog) and usually sits for the most part, as CTCSS in the first 300Hz of the signal being transmitted. DCS does take more bandwidth and it is more important for the radio to be on frequency due to the fact that much of the signal resides on the very bottom portion of the signal being sent. Also note, it is also known as Motorola Digital Private Line and again, the name Motorola comes up for a good reason. Below is the, much larger, table of used DCS codes.

DCS        
650125174255343445526703
751131205261346446532712
1553132212263351452546723
1754134214265356454565731
2165141223266364455606732
2371143225271365462612734
2572145226274371464624743
2673152243306411465627754
3174155244311412466631
32114156245315413503632
36115162246325423506654
43116165251331431516662
47122172252332432523664

Besides CTCSS and DCS there are some other tone signals out there. If you are really interested in these you can find a very nice PDF on the subject here: http://www.repeater-builder.com/tech-info/pl+dpl/tone_signaling.pdf

If you find something incorrect, have an update, or if there is something you would like to see added, drop me a line here. I like to keep things as up-to-date and as accurate as possible. Thank you! - Lucas / W6AER