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detection filtering. A sample of the BFO signal is made available to the frequency counter on the IF/BFO FREO
line for sideband frequency error determination.
9-8.
455KHz PLL.
For monitor frequency error determination a 455KHz Phase Locked Loop (PLL) is used
to filler and to shape the IF signal. The cleaned up signal is switched with the BFO signal to the frequency
counter.
9-9.
Scope Horizontal Control.
Switching for the scope horizontal input is divided between two modules.
The time base generator and the external horizontal input are selected on the scope amplifier module. The.
Horizontal Character Sweep Generator and the Synthesizer Sweep Generator signals are selected on the
Control Module to the INT SCOPE HORIZ signal line.
9-10.
For the dual display modes (characters and synthesizer sweep) the Horizontal Switch Control switches
the horizontal input between the synthesizer sweep and the character sweep. This switching occurs
simultaneously with that occurring in the scope vertical control as described in paragraph 9-6. The
Horizontal Switch Control also provides the SCOPE MODE EN line to the scope avplifier to enable the scope
mode horizontal inputs.
9-11.
Synthesizer Sweep Control.
The sweep signal generated by the Synthesizer Sweep Generator is
controlled in amplitude and in range across the front panel sweep width control. Attenuations of 1.0 or0.1 are
provided by the Sweep Width Select circuitry to the sweep signal at the DISPERSION SWP signal line to the top
of the width control. The bottom side of the width control is returned to the Sweep Width Select circuitry via the
DISPERSION SWP RTN line. A 10 to 1 resistor change is made in the return line simultaneously with the
altenuator change to give sweep ranges of 1-10 MHz and 0.01-1 MHz.
9-12. Scope Z-Axis Control. The SCOPE Z-AXIS signal has three possible sources as selected by the Z-Axis
Control circuit. For character displays the Z-Axis signal is the CHAR GEN Z-AXIS from the character
generator. The SWP BLANKING signal from the horizontal time base generator is switched to the scope Z-Axis
for the scope modes. For the remaining modes, spectrum analyzer and scope sweep, a logic zero level is gated
to the Z-Axis input.
9-13.
Modulation Display Control.
Internal modulation or demodulated signals are displayed on the scope
by switching the desired signal source to the input ranging switch and then switching the ranging switch
output to the scope vertical input. One of two modulation sources or a demodulation output can be switched to
the INT SCOPE TO RNG SW signal line for display on the CRT. Each of the signals are gain adjusted prior to
the selection switch for scope calibration.
9-14.
The DEMOD CAL AUDIO signal from the receiver is either AM, FM, or SSB as determined by the
operating mode. The peak signal level on this line is calibrated to 10kHz/volt forFM and 10%/volt for AM. SSB
signals are not calibrated.
9-15.
For AM the CARRIER+ MOD LVL input from the generator output detector provides a direct display of
the modulation. This input is a DC level representative of the average output level plus an AC signal
representative of the amplitude modulation on the output. For the scope modulation display the DC level is
blocked so that only the AC component is observed. This input is uncalibrated for absolute AC levels, butt he
processor by determining the peak AC and average DC levels can determine the modulation depth.
9-16.
For FM the MOO CAL AUDIO input from the audio synthesizer is calibrated to 5kHz/volt for narrow
band and to 20kHz/volt for wide band. Correspondingly the display calibrating attenuator has two gain ranges
to maintain the same display calibration for both narrow and wide band.
9-2
9-17.
Peak Detector.
Each of the modulation and demodulation inputs can be selected to the peak
detecting circuitry for the determination of% AM or kHz deviation. The peak detector circuitry provides DC
outputs equal to the negative and positive peak values of the input signal relative to the average DC level of the
signal. These levels are then digitized by the DVM and input to the processor where the modulation level is
determined.
9-18.
DVM Control.
Any one of ten internal or one external measurement point may be switched to the DVM
for level digitization. Switching is controlled by the processor so that measurements are made to provide
current display data. In general several measurement points must be input to obtain all the displayed data.
Therefore the processor continuously cycles the switch through the required inputs stopping at each one long
enough to digitize and input its level.
9-19.
The Internal DVM Select switch is followed by a range attenuator. As the processor cycles through the
inputs it sets the range attenuator according to the last cycle reading made at that input. Thus each internal
input is auto ranged over two decades to give three digit accuracy up to
a
maximum input of 10 volts. The
internal DVM inputs and their function are listed in table 9-1.
9-20.
External DVM inputs to the front panel jack are ranged by the processor over a four decade range
before being routed to the DVM switch. At the Internal/External DVM Select switch the external DVM FROM
RNG SW signal or the internal signal from the x0.1 Attenuator is selected to the DVM to A/0 signal line for
digitization.
9-3
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