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2-7.
AM, FM, CW, DSB Signal Generation. The built-in general purpose signal generator provides
continuous coverage of the HF, VHF, and UHF land mobile spectrum for receiver testing. Many forms of
external and internal modulation can be simultaneously impressed on the carrier signal for actual composite
signals. The frequency range of the RF signal generator is from 10kHz to 1000 MHz in 100Hz steps. Tt1e output
of up to 1 Volt rms provides sufficient amplitude to get through misaligned tuners and receivers. and is
especially effective when changing a receiver's frequency. The high level, clean output is available over the
entire frequency range of the Communications System Analyzer. The output frequency is referenced to an
internal time base which can be calibrated to the WWV Standard. (See paragraph 4-7.)
2-8.
Simultaneous Modulation.
Modulation is simultaneously available from an internal 1 kHz tone
generator, a multi-mode code synthesizer, and from external inputs. The external modulation can be voice
from a standard Motorola mobile radio microphone (which plugs into the front panel of the instrument). as well
as a signal applied to the external BNC input. Separate controls are provided for independently setting the
levels of the 1 kHz tone, the code synthesizer, and the external modulation sources. The 1 kHz test tone is a
convenient source of modulation for making SINAD measurements. A MOD OUT connector provides external
access to all of the modulation signals.
2-9.
Modulation Display.
The recovered audio waveform, or audio used to modulate the generator carrier,
can be viewed on the CRT. It is used to graphically measure deviation, and to aid in waveform analysis.
2-10.
Sweep Generation.
The sweep generator mode provides an RF output that is swept in frequency
across a band centered at the programmed frequency. A synchronized horizontal sweep for the internal
oscilloscope allows filter characteristics to be easily determined. This is ideal for in-depth troubleshooting of
IF amplifiers and filters.
2-11.
SINAD Metering.
A comprehensive check of receiver performance can be made with a SINAD
measurement. The analog line segment and digital representation of SINAD appear automatically whenever
the unit is in the normal generate mode. The only hookups required are from the Communications System
Analyzer to the RF input of the receiver under test, and from the audio output of the receiver to the instrument's
multipurpose input. The measurement, and appropriate servicing, can then be accomplished without the need
for a separate signal generator, SINAD meter or distortion analyzer.
2-12.
Multi-Mode Code Synthesizer. The Communications System Analyzer generates Private Line tones
(PL), Digital Private Line codes (DPL), two-tone sequential paging codes and tone-remote base signaling
tones. All codes are available at the Mod Out jack, as well as being used internally to modulate the RF signal
generator. This eliminates the necessity of using separate generators and oscillators for general servicing,
setting transmitter deviation, or for checking tone-remote-base control lines. Timing sequences are also
stored in the Tone Memory to provide fast set-up and eliminate errors. User programmable timing sequences
are also provided to allow the storage of non-standard or future time sequences.
2-13.
011-lhe-Air Monitor.
The 1.5
11
V sensitivity of the Communications System Analyzer receiver allows
off-the-air monitoring and measurement of transmitter frequency error and deviation to 1000 MHz. A variable
squelch allows weak signals to be monitored, but can be set higher to ensure the proper signal-to-noise ratio
for measurement accuracy. The off-the-air monitor function enables frequent parameter checks without
leaving the shop, thus spotting system degradation early and keeping service costs down. Bandwidth can be
set Wide for off-channel signal location or wide band FM; or Narrow for maximum sensitivity and selectivity.
2-14.
IF Display.
When the IF display mode is selected, the Communications System Analyzer's receiver IF
envelope is shown on the CRT. This allows the technician to qualitatively and quantitatively assess the
amplitude modulation envelope of a transmitter.
2-2
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 lo 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 varying 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:
lntermodulation 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 internal125 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 lor 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 of RF 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.
2-3
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