Motorola R-2001A, Service Manual

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detection filtering. A sample of the BFO signal is made available to the frequency counter on the IF/BFO FREQ
line for sideband frequency error determination.
9-8. 455 KHz PLL. For monitor frequency error determination a 455 KHz Phase Locked Loop (PLL) is used
to filter and to shape the IF signal. The cleaned up signal is switdhed 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 or 0.1 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
attenuator 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 timebase 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/voltforFMand 10%/voltforAM.SSB
signals are not calibrated.
9-15. For AM the C 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, but the
processor by determining the peak AC and average DC levels can determine the modulation depth.
9-16. For FM the MOD CAL AUDIO input from the audio synthesizer is calibrated to 5 kHz/volt for narrow
band and to 20 kHz/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