Associated with each row and column is a frequency. The telephone dialing pad acts as a 4-by-3 matrix (Figure 8.1). The program touchtone demonstrates how DTMF tones are generated and decoded. Virtually all modern VHF/UHF FM transceivers for amateur radio use include CTCSS encode and decode as standard features. basis for touch-tone dialing is the Dual Tone Multi-Frequency (DTMF) system. 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. Dual Tone Multi Frequency is a system of signal tones used in the field of communication whose application ranges from voice mail and help desks to telephone banking and controlling robotics designs. Voice communication systems are designed to use the frequency range of 300 Hz to 3 kHz, which allows for normal speech to be understood. We have use DTMF module (by Robo India) in this. Although we call these frequencies subaudible they are within the hearing range of most people. representing digits with tone frequencies, in order to transmit them over an analog communications network. 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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