Audio Board Operation - Aeroflex NAV 2000R Operation Manual

Aeroflex Operation Manual
The amplitude modulating audio signal is either generated internally by the NAV 2000R DSP board or
provided externally from the external audio input. On the audio board, the modulating audio signal level
is adjusted and monitored to generate the desired modulation percentage. Then, it is applied to a
temperature compensating amplifier on the RF board. This signal is then applied as a gain controlling
bias to a variable gain amplifier which acts as an RF modulator.
The modulated RF signal is amplified and the output is leveled by an automatic leveling control loop. An
audio detector in the automatic leveling control loop circuitry also provides the detected audio output.
After leveling, the modulated RF carrier is applied to a programmable step attenuator.
The programmable step attenuator circuit allows the output power to be programmed in 1.0 dB steps
while the leveling loop adjusts output power in 0.1 dB steps. The external audio modulation input is
provided on the rear panel. The modulator module also generates RF output high/low, audio input
high/low, and detected audio high/low (at 50% modulation with a single tone) indications to the NAV
2000R system computer. The system computer monitors these indicators to provide some self testing
during normal operation and during power on self test.

4.3.10 AUDIO BOARD OPERATION

The audio board accepts a fixed level audio signal. The level of this signal is adjusted and summed with a
DC voltage level to produce a 1 + modulation signal achieving the desired modulation percentage. It also
provides a bus interface for the RF modulator module to the NAV 2000R system computer. This enables
the system computer to control and monitor the module.
The audio signal input to the audio board can either be generated by the NAV 2000R DSP board or
applied via an external input. The external input may be switched on or off. It is AC coupled into the
modulator audio circuitry.
The RF Modulator Module Bus Interface circuitry provides the bus interface to the NAV 2000R system
computer. It consists of bus request/bus grant bus timing circuitry, RF modulator command decoding,
and RF module control signals.
The Modulation Centering & Calibration circuitry, Audio High/Low Indication circuitry, and % Modulation
Level Set Attenuator circuitry are used along with the Voltage Reference to provide a precisely calibrated
audio modulating signal to the RF Board.
The Audio High/Low Indication circuitry indicates whether or not the audio input amplitude has been
properly set. A single tone modulating signal is applied and if its peak falls one half percent above or
below the required peak amplitude, an indication is provided. The status of these high/low bits are
read by the NAV 2000R system computer.
NAV 2000R SIGNAL GENERATOR - REV. 0 – JULY 26, 2007 - PG 4-7