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e)
OPTIONAL PERFORMANCE VERIFICATION Of FCS Overshoot Compensator
1)
Connect
the oscillator to the junction of R806 and L801 ( this provides a
convenient injection point that bypasses the first clipper).
2)
Set
the
LIMITER
PROOF/OPERATE
switch ( on
Card # 6)
to
OPERATE.
3)
Observe the left rear- panel TEST JACK with
a scope. Set
the oscillator
frequency to 100Hz, and advance the oscillator output level until clipping just
barely occurs. Measure the oscillator output, and verify that it is approximately
0.63V rms. ( The " clipping" is the action of the overshoot compensator. If this
clipping
doesn't
occur,
then
there
is
a fault
in
the
overshoot
compensator
sidechain.)
4)
Increase the oscillator
output 4dB.
Substantial clipping should occur. Now
sweep
the oscillator frequency upward, and verify that the peak level of the
output
waveform
never
exceeds
the " flat- top"
level
of
the
100Hz
clipped
sinewave by more than 0.7dB, and that this 0.7dB peak occurs at approximately
4.4kHz.
At
this
frequency,
the
waveform
should
resemble
a filtered
square
wave with two equal cycles of ringing on the top and bottom of the wave ( Fig.
E-4).
If
substantially
more
than
0.7dB
overshoot
occurs,
particularly
if
the
ringing is not symmetrical, then suspect problems in the filters or phase- shift
networks associated with the FCS circuit.
Fig. E-4: 4.4kHz OVERDRIVEN FCS OUTPUT
f)
Repeat procedures ( a) thorough ( e) for the right channel ( Card # 9).
This concludes the Field Alignment Procedure for the entire OPTIMOD-TV system.
Insert the extender board in its slot, and replace the subpanel, being sure that all
four DZUS fasteners are fully tightened for RF suppression. Close the front
door,
and
fasten with its three screws. Remove the jumper between chassis and circuit
grounds, unless it is ordinarily used in your installation.
OPTIMOD-TV is now ready for reinstallation in the station.
E- E3
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