DANIELS
ELECTRONICS LTD.
TM
VHF Enhanced Extra Wideband Receiver Instruction Manual IM10-VR3H040-AB
3-1
3
THEORY OF OPERATION
Detailed circuit analysis and signal flow description for each of the three electronic modules;
Main Board, Enhanced Front End, and Synthesizer are provided in the subsections below. Refer
to Section 2, System Overview, of this manual for a description of the overall receiver operation,
and the receiver block diagram.
Refer to the appropriate drawings in Section 6 for each module.
3.1
21.4 MHz IF / Audio Main Board
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3.1.1
General
The 21.4 MHz IF / Audio Main Board accepts the low level IF signal from the Front End. This
processing includes: selective filtering, IF amplification, and final audio demodulation /
amplification. This board provides a high degree of receiver flexibility by providing a number
of different audio paths, audio levels, and control interconnect options. Refer to section 6 -
"21.4 MHz IF / Audio Main Board Schematic Diagram".
3.1.2
Power Supplies
The receiver operates from a main +9.5 Vdc source (from the system monitor) applied to B6 / Z6
at the main 48 pin connector. This source provides power to the Front End, local oscillator
module, IF amplifier, operational amplifiers, high level audio drive (U9), and internal regulators.
Regulator IC U1 pr6.0 Vdc to the IF / Audio Main Board demodulation IC U2.
Switching inverter supply U12 provides -6.0 Vdc to the squelch detection circuitry (U14, U16).
Operational amplifier U13B pr 4.75 Vdc for virtual ground generation.
3.1.3
IF Buffer Board
The IF Buffer board is required for Enhanced Front Ends only. SMB connector J7 provides IF
signal input from the Front End to the IF Port at 21.4 MHz. The IF Buffer board provides the
mixer on the Front End with a constant 50
Ω
load while providing a 50
Ω
source impedance to the
IF / Audio Main Board. L3 and C4 are series resonant at the IF frequency and provide a signal
path to the FET amplifier. C5 and L4 provide a shunt for frequencies other than the IF. The IF
Buffer board draws 30 mA of current.