Off-The-Air Monitor; If Display; General - Motorola R-2001A Service Manual

2-7. AM, FM, CW, DSB Signal Generation. The built-in general purpose signal generator provides
continuous coverage of the HF, VHP, 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 10 kHz to 1000 MHz in 100 Hz steps. The 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 Sl NAD 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.
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 withoutthe 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. Off-the-Air Monitor. The 1.5 u V sensitivity of the Communications System Analyzer receiver allows
off-the-air monitoring and measurement of transmitter frequency error and deviation to 1000MHz. A variable
squelch allows weak signals to be monitored, but can beset 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.
A comprehensive check of receiver performance can be made with a SINAD
2-2