Monday, July 12, 2010

I often see mentions of DTMF, CTCSS and DCS in QST, but I’m not sure what they mean ...

Q Bill Kendrick, WA6TMT, asks, “Can you define a couple of acronyms for me? I often see mentions of DTMF, CTCSS and DCS in QST, but I’m not sure what they mean.”

A DTMF: Dual-Tone MultiFrequency. Everyone in the country has encountered DTMF signaling, but they wouldn’t recognize it by that acronym. DTMF is better known to the masses as TouchTone. In the DTMF system two audio tones are combined whenever you press a button on a telephone or radio keypad. Both tones must be decoded on the receiving end for the signal to be “valid.” This provides a certain measure of reliability. In amateur applications DTMF is commonly used for remote control.

CTCSS: Continuous Tone-Coded Squelch System. Many hams know this one by the Motorola trade names Private Line, or simply PL. CTCSS uses individual audio tones of very low frequency. The frequencies are so low, in fact, they are below the normal receiver audio passband. This means that the tones can be sent along with voice audio without causing interference. A receiver with CTCSS enabled will be silent unless it receives a transmission that includes the proper tone. Repeaters often use CTCSS to control access in situations where there is interference from other repeaters on the same input frequency.

DCS: Digital Coded Squelch. This popular method of signaling uses a burst of data tones. As with CTCSS, a DCSequipped receiver will remain silent until it “hears” a data burst that it has been programmed to recognize.

From QST April 2000