-
monitor system voltages and discretes for fault conditions.

 2 The function of the signal processor is to:
_
 -compute and output, to the system processor, the ADF bearing derived from the ADF detector
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 -determine the presence of the ADF detector signal and flag the bearing data accordingly
 -detect the presence of a 400Hz or 1020Hz identification tone (or BFO mode) and output a "tone present" discrete to the maintenance processor
 -monitor ADF signal level status and output maintenance data to the system processor
 - output sin mode and cosine mode to the loop modulators via their respective D/A converters
 -process the ADF detector signal to provide filtered and amplitude controlled audio information to the aircraft audio system.
 (c)
 A maintenance processor assembly the primary function of which is the logging of maintenance information and secondarily, decoding the morse binary data stream into ASCII characters.

 (d)
 A power supply assembly which provides +12VDC, -12VDC and -5VDC from 115VAC at 400Hz.

 (e)
 A tuner/synthesizer assembly

 1_ The tuner combines the sense and loop signals from the
 antenna, amplifies and filters them and then provides the
 detected audio information to the signal processor.
 2_ The synthesizer receives frequency information from the system
 processor and provides fixed and variable oscillator signals
 for the mixers in the tuner.

 (4) Operation (Ref. Fig. 006A) The operation of the receiver is initiated when the desired frequency is selected by the FMGCs or RMPs. Frequency and function data are received via an interface. This data is used to activate the desired function, set the receive band and tune a Voltage Controlled Oscillator (VCO) for converting the received signal to the IF. Sense and loop signals from the antenna are applied to the loop modulators where they are modulated with 95Hz control signals from the signal processor. The summed output of the loops is corrected for the antenna loop gain and phase and then summed with the sense channel. The composite output of the summing circuit is passed through a band select filter, which output feeds the first mixer.
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 ADF Receiver - Simplified Block Diagram
 Figure 006A

R 1EFF : 051-051, 053-099, 106-149, 201-299, 1 34-53-00Page 29 1301-399, 401-499, 1Aug 01/05 1 1 1CES 1 The VCO is mixed with the input to generate a first IF of 15MHz. The signal is filtered and amplified and then applied to the second mixer where 18.6MHz mixes it down to a second IF of 3.6Mhz. It is once again filtered and amplified before application to a coherent detector. The output of the coherent detector is used to derive the AGC control for the IF. The composite audio is sampled and processed by audio and bearing algorithms in a Digital Signal Processor (DSP) in the signal processor area. The DSP filters the audio, and sets the output level and returns it to an audio amplifier stage, and then to the aircraft audio system. The DSP also applies a separate narrow audio filter and then detects the audio tone for MORSE ident. This binary data stream is sent to the maintenance processor for decoding into ASCII characters. The bearing is determined in the null-seeking algorithm by the DSP continuously adjusting the ratio of the 95Hz loop modulation applied to the sine and cosine modulators. When the ratio is properly adjusted, the amount of 95Hz present in the coherent detector output is minimized. The ratio of the loop modulation is then directly proportional to the raw bearing. The raw bearing is corrected for Quandrantal Error and calibration factors. The signal processor then converts this corrected bearing to ARINC word format and relays it to the system processor for transmission on the ARINC bus. In addition to its receiver control functions, the system processor continuously monitors receiver health and passes radio health information to the maintenance processor. It also initiates functional tests when conditions allow it. The maintenance processor processes commands from the CFDIU and stores faults detected by the system processor. It also decodes the MORSE ident data stream passed by the signal processor.

 **ON A/C 052-052,
 (3) Internal description The receiver determines the relative bearing to any selected transmitter operating between 190 and 1750 kHz. This bearing data is converted into ARINC 429 format and transmitted through ARINC buses to the DMCs. In addition the AM modulation of the carrier wave is detected and applied to the audio integrating system. The receiver is housed in an ARINC 2MCU case and consists of an aluminum chassis which contains:
　
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