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5-47.
The output signal from the IF filter has two possible paths. The path to the Log Amplifier and Detector
provides the spectrum analyzer capability. The other path is the linear IF Amplifier for AM, FM, and SSB
demodulation. The output level of the Amplifier is detected to give amplitude modulation and to provide the
AGC control on the IF amplifier. The IF signal is applied to the FM Demodulator and is senttotheScope/DVM
Control module (A3) for SSB demodulation and for frequency error determination.
5-48.
Demodulated audio from the selected demodulator is routed to the Audio Filter by the Select Switch
under processor control. The Audio Filter provides post detection filtering for both wide and narrow band
modes. The output of the Audio Filter is three signal lines. The Demod Calibration Audio line provides the
calibrated audio levels for modulation level determination. A Demod Audio output provides a level adjusted
signal to the front panel Demod Out jack. Speaker audio is level adjusted by the front panel volume control and
then amplified by the Audio Amplifier on the Receiver module.
5-49.
The Audio Amplifier sums the audio from the demodulator with the Alarm audio. The Audio Amplifier
provides a 0.5 watt output capability to the system's internal speaker. The Alarm generator is under the control
of the system processor.
5-50.
SSB demodulation is implemented on the Scope/DVM Control module by multiplying the 455kHz IF
signal from the Receiver with a signal from the Beat Frequency Oscillator (BFO). The BFO is controlled from
the front panel and typically has a frequency range of 455 ±3kHz. The BFO signal is switched with the output of
the 455kHz IF Phase Locked Loop (PLL) to the frequency counter for frequency error determination. The455
kHz PLL filters and shapes the IF signal to make it suitable for frequency counting.
5-51.
When in the spectrum analyzer mode the linear IF Amplifier is shut down and the Log Amplifier is
activated. The output of the Log Amplifier and Detector is a DC voltage that is proportional to the log of the 10.7
MHz IF input level. The log circuit has a dynamic range of approximately SO dB, covering input levels from -100
dBm to -20 dBm. The SPECTRUM ANALYZER signal from the Log Amplifier is the vertical input to the scope
for the spectrum analyzer display.
5-52.
Duplex Generator
5-53.
Simultaneous generate and monitor functions are available with the use of the Duplex Generator. The
frequency spread between generate and monitor frequencies is limited to a range of 0 to 10 MHz and a fixed
frequency of 45 MHz. A block diagram of the Duplex Generator function is shown in figure 5-7.
5-54.
The Duplex Output signal is generated by mixing the local oscillator signal for the first receive mixer
with a signal from the Offset Oscillator. The Offset Oscillator is at the frequency equal to the desired spread
between generate and monitor frequencies less the 10.7 MHz IF offset. The monitor function is unaffected by
the duplex mode and operates as described under paragraph 5-40.
5-55.
Frequency modulation of the duplex output is obtained by modulating the Offset Oscillator frequency
via the OFFSET MOD signal line. Control of the Offset Oscillator is directly from the front panel of the system.
A OFFSET FREQUENCY output from the oscillator provides an input to the frequency counter for the
determination of the duplex frequency.
5-14
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