(6) The limiter eliminates amplitude variations and passes the FM signal on to the
discriminator, which is sensitive to variations in the frequency of an RF wave. The resultant constant-
amplitude, frequency-modulated signal is then processed by the discriminator circuit, which transforms
the frequency variations of the signal into corresponding voltage amplitude variations. These voltage
variations reproduce the original modulating signal in a reproducing device, such as a headset,
loudspeaker, or teletypewriter.
(7) Frequency modulation generally is used by radiotelephone transmitters operating in the
VHF and higher frequency bands.
d. Radiotelephone.
(1) A microphone of a radiotelephone set converts voice or soundwaves (figure 10) to weak
electrical impulses. These impulses are strengthened by passing them through a series of audio
amplifiers and then through a modulator. The modulator provides the audio power necessary to
modulate the RF amplifier. At the receiver, the modulated RF is demodulated, allowing only the audio
component of the incoming signal to be reproduced by a loudspeaker or headset.
Figure 10. Examples of Voice-Sound Wave.
(2) Radiotelephone transmission is used extensively for communications with highly mobile
combat units, where speed of transmission is essential. It is used for person-to-person contact, where
security is not a limiting factor.
13
Previous Page
