Technical Description 4-4 X-2 Technical Service Manual
Publication No: 15-02047
4.2 Receiver
4.2.1 Input Filters
104-02908
The receiver input signal passes through the:
• selected PA low-pass filter
• transmit/receive relay K7
• 2 MHz high-pass broadcast filter to the Rx/Exciter & Control PCB.
4.2.2 First Mixer
104-02907 Sheet 1
The receive signal is applied to connector P1
[A1]
pins 1 and 2 on the
Rx/Exciter & Control PCB. It then passes through a 20 MHz low-pass filter
and transformer T1 to the input pins 12 and 13 of the first mixer IC1
[C3]
.
Mixer IC1 is a combined amplifier/balanced mixer with a gain of
approximately 20 dB. The received signal mixes with the output of Voltage
Controlled Oscillator VCO1 operating between a frequency of 47 MHz and
63 MHz, producing a balanced IF output centred at 45 MHz at pins 3 and
14.
4.2.3 45 MHz Roofing Filter
The 45 MHz IF signal is filtered through a 15 kHz roofing filter consisting of
T3, Z1, L10, Z2 and T4. This removes unwanted products produced by the
mixer. The filter output is applied to the balanced input pins 12 and 13 of
the second mixer IC8
[C7]
.
4.2.4 Second Mixer
Mixer IC8 is a combined amplifier/balanced mixer and identical to mixer IC1.
The 45 MHz signal mixes with the output of a second Voltage Controlled
Oscillator VCO2
[E7]
operating between 44.5435 MHz and
44.5455 MHz to produce a second IF centred at 455 kHz.
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