Service manual

Theory of Operation GPH-CMD VHF Radio
Page 4-4 BK RADIO
A. Power Amplifier
The Power Amplifier comprises two RF amplifier stages (see Figure 4-3 below). These are:
(1) Driver
(2) Integrated Power Module
Q1 U4
Driver
Stage
Power
Module
To
Harmonic
Filter
L.O. Input
(from VCO)
Power
Control
Figure 4-3 Power Amplifier Block Diagram
The Driver stage provides gain and isolation between the VCO and the Integrated Power Module.
The Integrated Power Module provides sufficient RF power to meet the radio's output power
specification after losses in the Harmonic Filter and Antenna Switch. The DC current into the
Integrated Power Module is monitored by the Power Control circuit.
B. Harmonic Filter
The Harmonic Filter attenuates the harmonics created by the Power Amplifier to meet or exceed
the transmit spurious and harmonic specification. The passband input and output impedances of
the filter are 50 Ohms.
C. Antenna Switch
The Antenna Switch connects either the Transmitter or Receiver to the antenna.
Figure 4-4 Antenna Switch Functional Block Diagram