Decoding The Secrets Of Ctcss - Baofeng UV-82 User Manual

Decoding the Secrets of CTCSS

While most rigs can send these low-frequency audio tones, decoding them is a handy trick,
too!
By Ken Collier, KO6UX
If you're an FM operator, you'll encounter CTCSS—Continuous Tone-Coded Squelch System—early in your ham career. You
may discover it while you're puzzling over the fact that a particular repeater seems deaf to your signals.
Like most hams, you'll probably check your Repeater Directory and determine that CTCSS is in use. No problem. Just program
your FM transceiver to send (encode) the proper audio tone and the repeater opens its doors to you. In most cases you won't hear
the tone because its frequency is quite low, near the bottom end of the range of human hearing. That's why you'll often hear CTCSS
tones referred to as subaudible—literally "below audibility."
This subaudible tone-control system was originally developed by Motorola and marketed under the name Private Line, or just PL
for short. To this day the tone frequencies established by Private Line remain the CTCSS standards (see Table 1). As a result,
many hams refer to CTCSS as "PL"—often without knowing what the letters stand for! You'll even hear PL used as a verb, as in,
"They PLed the repeater last month." (Translation: They installed CTCSS on the repeater last month.)
While many hams are familiar with the idea of sending a CTCSS tone to use a repeater, not everyone understands CTCSS
decoding. Virtually all modern FM rigs can send CTCSS tones, but only a few offer the ability to receive and process (decode) such
tones as standard equipment. CTCSS decoders are usually available as options.
If you're about to purchase an FM transceiver, should you shop for a rig that includes CTCSS decoding? If the radio you already
own offers a CTCSS decoder as an option, should you install it?
Table 1—CTCSS Frequencies (Hz)
69.3
71.9
74.4
77.0
79.7
82.5
85.4
88.5
91.5
94.8
97.4
100.0
103.5
107.2
110.9
114.8
118.8
123.0
127.3
131.8
136.5
141.3
146.2
151.4
156.7
162.2
167.9
173.8
179.9
186.2
192.8
203.5
210.7
December QST: Decoding the Secrets of CTCSS - Page 1
ARRL 1996 QST/QEX/NCJ CD C i ht (C) 1997 b Th A i R di R l L I