Raytheon Pathfinder 1200 Instruction Manual page 68

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6) Circulator and Diode Limiter
A ferrite circulator is used for the duplexer. The Passive Diode Limiter is used
to protect the receiving section (especially the mixer diodes). From excessive RF
input levels at all times.
7) Gunn Oscillator
A Gunn Oscillator is used for the local oscillator. The oscillator generates a low
energy RF signal the frequency of which is tuned 38 MHz higher than that of the
transmitter output frequency.
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8) Mixer
Two small diodes, fitted inside the mixer waveguide assembly at the, receiver
input, form a balanced mixer which feeds the intermediate 38 MHz frequency signal
to the 1. F. amplifier.
9)
1. F. Amplifier
The 1. F. amplifier consists of two stages. The first stage is a low noise transistor
amplifier; the second is a linear integrated circuit amplifier stage. The second stage
is controlled by the GAIN-SEA CLUTTER signal from the display unit.
10) Detector
In this stage, the 1. F. (38 MHz) component is removed leaving video rate signals
for display.
11) Video Circuit
This circut is primarily an emitter follower which feeds the video signal from
the detector to the display unit providing an impedance match to the coaxial cable.
At the same time this emitter follower supplies the video integrator circuit used for
tuning of the Gunn Oscillator.
6.1.3 Display Unit
The display unit consists of the main control circuits, the control panel circuitry,
the CRT display and the power supply.
The display unit is fed with the video and bearing synchronizing signals from the
scanner unit via a multicore cable. Semi-conductors and integrated circuits are used
throughout the display except for the CRT and lamps.
1) Video Circuit
The video circuit consists of the FTC (Rain-Clutter) circuit, inverting amplifier,
D.C. restorer circuit, emitter follower and tuning indicator circuit.
2) Comparator
The comparator generates a digital pulse train from the input analog video signal.
Comparator level adjust RV402, sets the video threshold.
3) Pulse Stretch
The pulse stretch circuit expands the width of the digital video pulses, according
to the range scale selected.
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