![]() Typical uses are mobile radio paging, selective calling, and other various. Virtually all modern VHF/UHF FM transceivers for amateur radio use include CTCSS encode and decode as standard features. PC Programmable DTMF (Touch-Tone) decoder interfaces with all FM transceivers. As long as we filter out the frequencies below 300 Hz before the signal gets to the radio speaker, the user won’t notice the presence of the CTCSS tone, but we’ll still have the desired voice frequencies. Voice communication systems are designed to use the frequency range of 300 Hz to 3 kHz, which allows for normal speech to be understood. Although we call these frequencies subaudible they are within the hearing range of most people. Because the tone is active the entire time the transmitter is on, we’d like to keep it from being heard in the receiver. To keep the transmitter from over deviating, we usually set the tone deviation at around 600 to 800 Hz. This means that the tones will be present with the normal voice signal. Unlike DTMF tones, which are sent momentarily as the key is pushed, CTCSS tones are sent any time the transmitter is on. The CTCSS frequencies are in the range of 67 Hz to 254 Hz. ![]()
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