CTCSS stands for Continuous Tone Coded Squelch System, often referred to as “PL” (Motorola’s trade name) or “Channel Guard” (Ericsson/GE’s trade name). Many repeaters require the use of a CTCSS to access the repeater. It is also known as “sub-audible tone” because its frequency is at the lower end of or just below the range of hearing of most humans.
Contrary to popular belief, most repeaters that require the use of a specific CTCSS tone to access the repeater are NOT closed repeaters. CTCSS is often used as a means of solving an interference problem or preventing one. Some repeaters may also generate a CTCSS tone on the repeater output so that repeater users who are equipped with a radio capable of decoding sub-audible tones will not hear other interference sources on the channel that would otherwise open the squelch of the user’s radio.
It is up to the owner/trustee of the repeater to decide whether or not to make public the sub-audible tone for a particular repeater. SERA honors the desire of the owner/trustee in publishing the CTCSS code only when so requested. We highly recommend that, where possible, tones be published.
We strongly recommend the use of CTCSS on all repeaters’ receivers. CTCSS is a minor inconvenience when you consider how many potential problems it can eliminate. The use of CTCSS may be required for a coordination to be granted if conditions so warrant, such as proximity to a co-channel repeater, or in an area where band openings frequently aggravate co-channel interference problems.
The SERA recommends regional CTCSS tone plans in the hopes that repeater owners/trustees in a given area will standardize on a particular CTCSS tone for that region. The reason for this is to make it easier for users to operate the local repeaters, as some older radios are only capable of a single tone as compared to modern radios which can have sub-audible tones selected on a per-channel basis. Consult with your local coordinator for recommendation on a CTCSS tone for your repeater.
This chart shows each sub-audible tone’s two-character alphanumeric designator and corresponding tone frequency in Hertz
CTCSS Tones & Designators
| XZ | 67.0 | 1B | 107.2 | 6A | 173.8 |
| WZ | 69.3 | 2Z | 110.9 | 6B | 179.9 |
| XA | 71.9 | 2A | 114.8 | 7Z | 186.2 |
| WA | 74.4 | 2B | 118.8 | 7A | 192.8 |
| XB | 77.0 | 3Z | 123.3 | M1 | 203.5 |
| WB | 79.7 | 3A | 127.3 | 8Z | 206.5 |
| YZ | 82.5 | 3B | 131.8 | M2 | 210.7 |
| YA | 85.4 | 4Z | 136.5 | M3 | 218.1 |
| YB | 88.5 | 4A | 141.3 | M4 | 225.7 |
| ZZ | 91.5 | 4B | 146.2 | 9Z | 229.1 |
| ZA | 94.8 | 5Z | 151.4 | M5 | 233.6 |
| ZB | 97.4 | 5A | 156.7 | M6 | 241.8 |
| 1Z | 100.0 | 5B | 162.2 | M7 | 250.3 |
| 1A | 103.5 | 6Z | 167.9 | 0Z | 254.1 |
SERA CTCSS District Plans
50 MHz thru 1.2 GHz
Pool #1: (TN-East & NC-East)
67.0 88.5 118.8 156.7 206.5
Pool #2: (WV, TN-Middle & SC)
69.3 91.5 123.0 162.2 210.7
Pool #3: (NC-West)
71.9 94.8 127.3 167.9 218.1
Pool #4: (GA-South, TN-West & VA-East)
74.4 97.4 131.8 173.8 225.7
Pool #5: (MS-South, KY-West & VA-West)
77.0 103.5 136.5 179.9 229.1
Pool #6: (KY-East, GA-North & MS-North)
79.7 107.2 141.3 186.2 233.6
Pool #7: (Common Pool 1)
82.5 110.9 146.2 192.8 241.8
Pool #8: (Common Pool 2)
85.4 114.8 151.4 203.5 250.3
Common Tone 1: 100.0
Common Tone 2: 254.1
29 MHz only
Region W4 146.2 (4B), 100.0 (1Z), 82.5 (YZ), 186.2 (7Z)
Region W5 151.4 (5Z), 103.5 (1A), 85.4 (YA), 192.8 (7A)
Region W8 167.9 (6Z), 114.8 (2A), 77.0 (XB), 203.5 (M1)