Your modem takes what's coming down this wire and separates out each individual frequency, using both of them to generate the tones. This tip wire actually carries both sides of all frequencies at once. When you press any number on your keypad or dial pad, current flows through that wire in order to generate its specific frequency (1=1209+901 Hz). The tip side goes to your telephone handset when you pick it up, which sends an electrical current down that wire into your earpiece, creating sound. Here is a simple explanation of how it works :Įach phone line has two wires in it - one for the 'tip' part of the signal, and another one for the 'ring' part of the signal. It is of note that repeaters are often used to filter out DTMF tones so they don't go through the repeater, so you won't hear them on the repeater output.
The DTMF deviation for FM, such as 2.5 kHz peak deviance, should be 1.65 Hz or less if you are using it.ĭTMF signals are an “in-band” signaling system, so we'll typically hear the tones being sent over the air if we just listen on the frequency. Most repeater operators I know choose 2.5 to 3.0 kHz as their DTMF deviation. The general guideline is that the DTMF error should not be more than two-thirds of the maximum variation (2/3rds of 5 kHz equals 3.33 kHz). Most radios are set to the manufacturer's specifications at the factory and do not require any user adjustments.įor most amateur FM systems, we use a peak deviation of 5 kHz. DTMF can also be used to call or notify another station on a selective basis.ĭistortion can prevent any tone communication system from being correctly received, so DTMF levels should not be excessively high.
Mobile setups have a keypad incorporated into the microphone, while handhelds have a keypad on the front of the device.ĭTMF for handheld radios are tones on radios that are frequently utilized to transmit instructions via radio waves, such as repeater control, autopatch access, and IRLP access.
Modern FM radios include a DTMF encoder as part of the radio.
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