Motorola R-2001A, Service Manual, Page: 20 / 220

2-15. Spectrum Analyzer. In this mode of operation the CRT displays a window of the RF spectrum whose
bandwidth (from 1 MHz to 10 MHz) is determined by the DISPERSION/SWEEP control. The center frequency
of this window ranges from 4 MHz to 1,000 MHz, selectable by entering a specific center frequency with the
keyboard. This center frequency is digitally displayed at the top of the CRT screen, eliminating the need for an
external signal generator, and counter to provide markers. Once a signal is centered on the screen, positive
identification is aided by switching the Analyzer to MONITOR AM or FM and listening to the demodulated
output via the built-in audio amplifier and speaker. The spectrum analyzer's center frequency can be scanned
up or down at rates vary ing from 0.5 kHz per second to 5 MHz per second, using the RF scan control. Slow rates
are used to precisely determine a subject signal's frequency while faster rates are used for locating intermittent
transmissions or viewing large areas of the spectrum in a short time. Uses of the Spectrum Analyzer
are: Intermodulation interference identification, IF and RF signal tracing, transmitter harmonics
measurements, transmitter spurious checks, and receiver local oscillator radiation.
2-16. RF Burnout Protection. At RF input levels above 200 mW, in any operating mode, the input
automatically switches to the internal 125 watt RF load, thus protecting the attenuator and signal generator
against damage from a keyed transmitter. If power above 200 mW is applied in any mode except the power
monitor mode an audiable alarm sounds and a visual warning on the CRT directs the operator to switch to the
power monitor mode.
CAUTION
To prevent undue stress on the protected circuits it is advisable to always switch the
system to the power monitor mode before applying power in excess of 200 mW.
Additional protection is also obtained by making it a practice not to leave the step
attenuator in the 0 dB position.
2-17. Terminated RF Power Measurement. RF power is automatically measured when the Communications
System Analyzer is in the Power-Monitor mode. The built-in RF load dissipates up to 50 watts for three minutes
and up to 125 watts for one minute. If a high power transmitter should be keyed into the unit for a time long
enough to threaten overheating of the power measuring circuitry, the audible alarm sounds and the CRT
display changes to read "RF LOAD OVER-TEMP," thus warning the technician to un-key. This instrument
function is further enhanced by the simultaneous indication ofRF power output, carrier frequency error, and
modulation, all on the same CRT display.
2-18. In-Line Power Measurement. Use of the Motorola ST-1200 series Wattmeter elements in conjunction
with the analyzer's external wattmeter display provides measurement of forward and reflected antenna power
on the CRT display. This capability eliminates the complex hook-ups and the additional instruments normally
required for antenna measurements.
2-19. Duplex Generator. In this mode, the Communications System Analyzer simultaneously receives and
generates the signals for duplex radio servicing, while generated and monitored frequencies are observed on
the CRT. In the 0-10 MHz range, the'Freq. Set'control tunes the proper offset frequency for the VHF and UHF
bands. The 45 MHz mode provides a single offset for the 800 MHz range. A switch is also provided to select high
or low side offset, as required. The Duplex Generator provides enhanced capability to service equipment such
as repeaters, car telephones and Emergency Medical Telemetry portables.
2-20. 500-kHz Oscilloscope. This general purpose scope is ideal for waveform analysis in two-way
communication servicing. Use it for viewing modulation signals (either internally or externally generated),
detection of asymmetric modulation or audio distortion, and general purpose signal tracing and
troubleshooting.
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