Operating instructions

Theory of Operation DMH Series VHF Radio
Page 4-4 BK RADIO
C. Front End
The preselectors are varactor-tuned direct coupled filters. The preamp Q7 provides gain to
overcome filter losses and provide good noise performance.
D. Front End Tuning
U2 is a digital to analog converter that provides tuning voltages for each of the five varactor
elements in the pre-selectors.
E. Mixer/IF
The mixer converts the RF input signal to an intermediate frequency of 16.9 MHz where it is
filtered and amplified.
F. IF Amp
Q6 provides gain for the IF signal.
G. IF Processor
U1 further processes the IF signal before application to the Baseband Signal Processor.
4.3.3 HIGH LEVEL PA BOARD
A. Power Amplifier
The high level power amplifier consists of an integrated VHF power module.
B. Harmonic Filter
A filter is used to attenuate transmitter harmonics before they reach the antenna port.
To
Harmonic
Filter
Power
Module
Driver
Stage
L.O. Input
(from VCO)
Power
Control
U103
Q102