Figure 3-8.—Radio transmitter unit.

3-9 Figure 3-8.—Radio transmitter unit. When the AM and ssb transmit modes of operation are used, the output from a handset is applied to the transmitter. The voice signals are amplified and used to modulate a 500-kilohertz local carrier that produces a 500-kilohertz IF. The resulting double sideband signal is filtered in the AM mode, amplified, and converted by a triple-conversion process to the desired rf operating frequency. The rf signal is amplified to a nominal 100 milliwatt level. In cw operation, the 500-kilohertz local carrier is inserted directly into the IF amplifiers. The signal is further processed in the same manner as the voice signals in the AM or ssb modes of operation. In fsk operation, the loop current is converted to audio frequencies representing marks and spaces. These audio signals are applied to the audio circuits of the transmitter. Thereafter, these signals are processed in the same manner as the voice signals in AM or ssb modes of operation. A typical radio transmitting set block diagram is shown in figure 3-9.