3-21
Figure 3-20A.—Cw compared to an rfcs teletypewriter signal.
Figure 3-20B.—Cw compared to an rfcs teletypewriter signal.
AUDIO FREQUENCY TONE SHIFT.—Tone-modulated (afts) systems use amplitude modulation
to change dc mark and space impulses into audio electrical impulses.
A basic tone-modulated system is shown in figure 3-21. Conversion to audio tones is accomplished
by an audio oscillator in the tone converter. Rapid varying of the tone, according to the characters
transmitted from the teletypewriter equipment, amplitude modulates the carrier wave in the transmitter.
The receiver receives the modulated signal and separates the audio signal from the carrier. This process of
separating the modulated signal is known as detection or demodulation.
