Technical data

Aeroflex Operation Manual
NAV 2000R SIGNAL GENERATOR - REV. 0 – JULY 26, 2007 - PG 4-12
The software on the system computer board passes control words to and reads status from, the DSP
board and the Modulator assembly.
The information passed to the Modulator tells the modulator the % MOD to output, and the audio source
and conditioning to be used. The status passed back from the modulator allows the system software to
monitor the modulator operation.
The information passed to the DSP board tells the DSP board the operational mode, the audio
frequencies to be generated, the phase relationship of these signals, the amplitude relationship of these
signals, and Morse code characters and timing to be used. The status passed back from the DSP allows
synchronization of variables passed and allows the system software to monitor the DSP operation.
The DSP software is downloaded from the system computer on power up. The DSP runs this software to
actually generate the audio signals.
4.4.1 SELF TEST
The NAV 2000R performs a self test during power up. This self test includes the following checks and
measurements.
The CPU board reads, calculates, and compares the calculated checksum with the stored checksum
within EPROM, EEPROM (UV BOOT and DYNAMIC ROM), and Battery RAM. It also writes and reads
patterns to the operational RAM (STATIC) to verify its functionality. The CPU then writes and reads the
DSP board RAM (PROGRAM BOOT ram) to verify it. The DSP program is then transferred to the DSP
RAM. Upon the CPU releasing the DSP reset, the DSP processor reads, calculates and compares a
stored checksum with the calculated checksum of the SINE look up ROMs residing on the DSP board.
The DSP processor writes these test results into a status register. The CPU board displays the results of
the ROM and RAM tests on the SYSTEM DIAGNOSTICS NAV 2000R display.
The MODULATOR is checked next. To do this the CPU board tells the DSP board to generate a single
1000 Hz tone, and tells the modulator to produce a depth of modulation of 50.0 %.
The CPU board then reads the status bits of the modulator to verify the following: 1) Audio level outputted
by the DSP and received by the modulator is the proper level. 2) Recovered audio out of the Modulator
diode detector is proper for 50.0 % AM modulation. 3) The AGC control voltage of the RF OUTPUT
leveling circuit is within its normal range. The CPU then displays these results on the SYSTEM
DIAGNOSTICS display.
For all Modulator tests to pass, the modulator must have the RF IN signal applied at approximately the
proper level and within the NAV 2000R frequency band. With no RF applied the RF level and detected
Audio test will fail indicating outputs too low.
NOTE:
The self test discussed above is fully performed during normal operation. But if the FORCE BYPASS ON
POWER UP configuration is selected, a shortened self test is performed. The last two steps of the
MODULATOR tests; DETECTED AUDIO and RF LEVEL, are not performed. With RF switched off from
the modulating circuitry these tests will always fail.