Sinad Meter - Motorola R-2001A Service Manual

preamp on. the Front Panel Interface module (A12). The preampprovittes (he required horizontal input
sensitivity and buffers the signal to the select switch on the Scope Amplifier module.
5-90. Internal horizontal signals, Sweep Generator and Character Sweep outputs, are selected on the
Scope/DVM Control module (A3). The Sweep Generator provides a sawtooth waveform to the RF Synthesizer
module for the sweep generator and spectrum analyzer functions. The sweep signal to the CRT horizontal
input causes the scope sweep to be synchronous with the synthesizer sweep for the spectrum and swept filter
response displays.
5-91. The Horizontal Character Sweep generator output is a sawtooth waveform that provides the horizontal
sweep for the raster scan character display.
5-92. One of four possible vertical signal sources are switched to the Vertical Amplifier input by a Select
Switch on the Scope/DVM Control module. The 455 kHz IF and SPECTRUM ANALYZER signals from the
Receiver Module provide the IF envelope and spectrum analyzer displays respectively. The Vertical Character
Sweep generator gives the vertical sweep for the raster scan character display. The remaining input is the path
for external vertical or modulation scope vertical inputs from the Front Panel Interface module.
5-93. A vertical preamplifier on the Interface module gives a vertical sensitivity of 10 millivolt per division and
provides positioning and vernier gain capability for its input. The amplifier is proceeded by a four decade range
attenuator which is controlled from the front panel vertical switch through the processor. The attenuator
provides external vertical input sensitivities from 0.01 to 1.0 volt per division and modulation scope sensitivities
from 0.25 to 25 kHz per division.
5-94. A Select Switch ahead of the Attenuator selects between the external vertical input or the modulation
scope inputs. The External Vertical input path is further selected between AC and DC coupling before
becoming the vertical input jack on the front panel. The modulation scope signal path is switched to one of
three possible sources on the Scope/DVM Control module. Demodulation signals from the Receiver are
selected via the DEMOD CAL AUDIO path, and frequency and amplitude modulation signals via the MOD CAL
AUDIO and CARRIER + MOD LVL signal paths respectively. The Audio Synthesizer module provides the MOD
CAL AUDIO signal while the RF Input module gives the CARRIER + MOD LVL signal.
5-95. A Z-Axis Select circuit on the Scope/DVM Control module gates either the CHARACTER GEN signal
for character displays or the retrace blanking signal from the Time Base Generator for scope displays to the Z-
Axis Modulator on the Scope Amplifier module.
5-96.

Sinad Meter

5-97. Sinad, which is defined as the ratio of noise plus distortion to signal plus noise plus distortion, is a
measurement of the audio quality at a receiver output. Measurement of the Sinad is implemented with a 1 kHz
notch filter. For a receiver receiving a 1 kHz tone the audio output is applied to the 1 kHz notch filter. Sinad is
then the ratio of the signal power at the output of the notch filter to the signal power at the input of the notch
filter. A block diagram of the Sinad Meter is shown in figure 5-12.
5-98. The Sinad Input from the front panel is AC coupled to the range Attenuator on the Front Panel Interface
module (A12). Processor control on the Attenuator allows a wide range of input levels to be automatically
handled. The output of the Attenuator is routed to the 1 kHz Notch Filter on the Scope/DVM Control module
(A3). Detectors, comprised of fullwave rectifiers and filters, on the input and output of the notch filter
determine the respective power levels.'The DC outputs of the detectors are read by processor through the
DVM. The processor determies the ratio between the two readings and displays the Sinad.
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