VOR Receiver - Simplified Block Diagram
 Figure 007A

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 34-55-00Page 31 1401-499, 1Aug 01/05 1 1 1CES 1

 MARKER Receiver - Simplified Block Diagram
 Figure 008

R 1EFF : 001-049, 101-105, 151-199, 1 34-55-00Page 32 1 1 May 01/05 1 1 1CES 1 The recovered marker audio is then amplified and passed through an anti-alias (low-pass) filter to reduce harmonics before it is output to the main processor for analog-to-digital conversion. Functional testing is accomplished by applying a test enable signal through a buffer which provides a constant voltage to the base of the test oscillator transistors to prevent variation in the power levels of the test oscillators. The test oscillator injects a 75 MHz signal into the receiver through an adjustable pad which is used to set the output power level for maximum receiver sensitivity.

 (c)
 Instrumentation The CPU section is used to process the data from the DSP section, to provide information to the front panel display and to provide the data and control signals to the I/O section. The microprocessor in the CPU section controls all major functions of the VOR Receiver. ASICs an PLDs serve as the microprocessor controller and provides the interfaces with the memory devices (boot routine, program, fault and data), the data loader/recorder card, and the front panel display driver. Data is exchanged with the DSP section through a dual-port RAM.

 (d)
 LRU monitoring The maintenance processor, monitors the health of the VOR and marker beacon receivers. The maintenance processor provides all the BITE functions for the LRU. BITE information is transferred to the system processor for communications to the aircraft maintenance functions include:

 1_ Receive data from the ARINC maintenance bus and store the
 time, data, aircraft IDENT, aircraft configuration and process
 the maintenance control word.
 2_ Process data received from the system processor for storage in
 the Non-Volatile fault Memory (NVM).
 3_ Monitor discrete inputs.
 4_ Determine the validity of the maintenance input control word.
 5_ Format the fault summary word and transfer it to the system
 processor.
 6_ Transfer all OMS interactive mode data and normal mode data
 words to the system processor.
 7_  Provide maintenance menus in the aircraft.

R 1EFF : 001-049, 101-105, 151-199, 1 34-55-00Page 33 1 1 May 01/05 1 1 1CES 1 8 Provide extended interactive mode support for troubleshooting

_ when the LRU is in the maintenance mode.

R **ON A/C 051-099, 106-149, 201-299, 301-399, 401-499,
 (3) Operation
 (a)
 VOR operation (Ref. Fig. 007A) The antenna applies the composite signal transmitted by the ground station to an RF receiver. In the receiver, the signal passes through a low-pass filter, a bandpass filter (preselector) and an RF switch to an RF amplifier. The output of the amplifier passes through one of two bandpass filters, depending on the RF frequency of the station being received, to the first mixer. The mixer combines the RF signal with a Local Oscillator (LO) to produce a first Intermediate Frequency (IF) of 20.05 MHz. The first LO injects a frequency 20.05 MHz below the desired RF frequency. The mixer output is filtered by a crystal filter and passed through a two-stage IF amplifier. Following the IF amplifier, the signal is mixed with a 20.505 MHz second LO to produce a second IF of 455 MHz. The second IF signal is demodulated using a precision AM peak detector. The VOR detector signal is processed by the signal processor on the instrumentation module. The filtered VOR detector signal is output to the rear interconnect module where it is amplified and output to the aircraft.

 (b)
 MARKER operation (Ref. Fig. 008A) The RF signal is filtered through a low-pass and a 75 MHz bandpass filter. Following the bandpass filter, the signal passes through an RF switch. This switch selects the incoming signal or the functional test signal. After the switch, an RF amplifier provides 12 dB of gain. Following the RF amplifier, the signal is further filtered by another 75 MHz bandpass filter. The output of the second filter goes to a mixer, where it is mixed with an

 85.700 MHz Local Oscillator signal to produce an IF of 10.7 MHz. This IF signal is filtered, amplified and demodulated. The detector output is applied to three tone filters. The filter outputs are rectified and checked against a reference level by a comparator. Each comparator output is sent to the instrumentation module.
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 MARKER Receiver - Simplified Block Diagram
　
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