MAINTENANCE MANUAL
IFR 4000
2-2-1
Page 13
Aug 1/04
The received signal bypasses the power amp through the RF switches, through the LOC
coupler to the coupler that feeds the frequen cy counter. Part of the received signal is
coupled off to provide the input for the frequency counter circuitry. A log amp chip acts as
a limiter, providing the input to a PLL chip that is used as a prescaler for the frequency
counter. The PLL chip provides a programmable prescaler, with the output sent to the
FPGA on the Multi-Function PCB Assy. In addition, the video output of the log amp is feed
to an analog to digital converter that is used as a software controlled threshold.
The receive signal passes through the attenuators, which can be used as part of a coarse
AGC (if needed). The signal bypasses the generate amp and is input to the mixer via the
low-pass filter. The signal is mixed with the LO to produce a 450 MHz IF. The bandpass
filter filters out unwanted mixer products. The RF switch steers the signal to the mixer
section of the IF receiver chip. The LO for the mixer is provided by the DDS/PLL
synthesizer, that is tuned to approximately 450 MHz, to give a 455 kHz IF. The 455 kHz IF
is filtered and input to the Log amp section of the IF receiver chip. The Log amp provides a
limited IF signal, used for FM demodulation, and a detected video output used for
thresholding.
Summary of Contents for IFR 4000
Page 1: ...NAV COMM Test Set Maintenance Manual 1002 5600 4P0 IFR 4000...
Page 3: ...MAINTENANCE MANUAL IFR 4000 FOR QUALIFIED SERVICE PERSONNEL ONLY...
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Page 166: ...MAINTENANCE MANUAL IFR 4000 2 3 1 Page 6 Aug 1 04 STEP PROCEDURE 4 Remove the Fuse...
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