3-34
channel. A mark in an individual tty loop keys an audio tone 42.5 hertz below the center frequency. A
space in the input signal keys an audio tone 42.5 hertz above the center frequency. Let's look at an
example. The mark and space frequencies for channel one are calculated as 382.5 hertz and 467.5 hertz,
respectively (425
42.5). Combining these keyed tones into a composite signal results in a tone package
within a standard 3,000-hertz bandwidth. By occupying no more than 3,000 hertz of the audio spectrum,
the output signal is suitable for transmission via radio or landline.
Figure 3-31.—Block diagram of modulator units.
Q28. What is the function of a tone terminal set?
Q29. What are the two types of multiplexing?
Q30. What is the purpose of multiplexing?
