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The
deemphasized THD+Noise should not exceed 0.1% at
any frequency
except
5kHz, where up to 0.25% is acceptable. ( The increase in distortion at 5kHz is a
subtle artifact of the PROOF mode in the Hilbert- Transform Clippers, and does
not
represent their performance in OPERATE mode. If you are interested in a
further explanation, see paragraph 5.b of Appendix B.)
In
many cases,
measured results will
be
determined entirely by the
quality
of
oscillator and distortion analyzer available, and/or by the presence of RF
fields
which might affect the instruments.
6)
Noise: Short both OPTIMOD-TV inputs, and measure the deemphasized noise
at
the OPTIMOD-TV
MAIN
OUTPUT.
It
should not exceed - 63dBm. ( Note
that
hum
or
buzz
due to test
equipment
grounding problems and/or high RF
fields
may
result in falsely high readings. If the output of the Ni&D set
is monitored
with a scope, problems like this should be immediately apparent.)
c)
Operate- Mode
Measurements:
These
measurements
evaluate
certain
static
characteristics
of
OPTIMOD-TV
in
its
normal
OPERATE
mode.
Normal
measurements
given
herein
are
provided
for
service
guidance
only
and
are
not
guaranteed.
As
in
the
PROOF
mode
measurements
above,
these
measurements
should be repeated for both left and right channels.
1)
Reconnect
the
audio
oscillator
to
the
OPTIMOD-TV
input.
Switch
both
PROOF/OPERATE
switches
to
OPERATE.
Be
sure
that
operating
controls
are
standardized as described in ( a) above. Set the oscillator frequency to lkHz, and
adjust
the oscillator output level until the TOTAL MASTER G/R meter on the
front panel reads " 0" dB.
2)
Verify that the OPTIMOD-TV VU meter reads 0 VU + 0.5VU in the COMPR
OUT position.
3)
Change
the
setting
of
the
CLIPPING
control
to "- I" ( 12:00)
to
avoid
the
normal sinewave clipping which ordinarily occurs when the CLIPPING control
is
set
beyond "- I",
and which would otherwise
mask
actual problems which might
exist.
Measure the OPTIMOD-TV output level and THD at the MAIN OUTPUT for each
frequency indicated in the table below, and compare your results with the typical
readings provided.
TABLE D-2
FREQUENCY ( Hz)
RESPONSE ( Vrms/flat)
RESPONSE ( Vrms/deemph)
THD (%)
50.0
100.0
1.0K
3.0K
12.0K
1.70V
1.80V
2.10V
2.40V
2.70V
1.65V
1.80V
1.90V
1.40V
0.45V
0.07%
0.07%
0.02%
0.04%
0.02%
NOTES:
1. THD measured with deemphasis.
2. CLIPPING control set to "- 1" ( i.e.,
12:00).
3. THD highly sensitive to setting of CLIPPING control.
4. Increase in THD at 50Hz due to " Bass" band clipper action.
The increase in THD at 50Hz is caused by the action of the " Bass" band clipper
located
between
the
first
and
second
sections
of
the
bass
crossover (see
paragraph 2.b in Appendix A). By setting the threshold of clipping low enough so
that a small amount of harmonic distortion is produced with sinewave test signals
(unrepresentative of speech or music), the action of the clipper is optimized with
respect
to program
material.
This prevents audible IM between bass and high -
frequency program material from occurring in the peak limiting circuitry which
follows the preemphasis and HF limiting.
D-3
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