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transmission system; for instance, in a “composite” STL, or even in a
long run of coax cable. The following procedure leaves the 708 adjusted
for
its own
best stereo separation. Nevertheless, the front-panel
MPX
EQUAL
. control will give a user the option of optimizing the entire
transmission system, though he should keep in mind that a chain is
only as strong as its weakest link. It’s far wiser to fix the weak link
than to accommodate for it at another point.
1. The
COMPOSITE OUTPUT
of the 708 should be cabled directly to
the composite input connection of the Mod-Monitor using a short
cable of known characteristics, preferably 50-ohm or 75-ohm coax.
2. Preset the 708 as follows:
MODE — STEREO
PILOT — ON
O’SHOOT COMP. — OUT
PRE-EMPHASIS — OUT
COMPOSITE PROCESSING — OUT
1. Apply a 1.5kHz sinewave signal from the Audio Generator to the
708
left
channel
PROGRAM LINE INPUT
only
. Set the signal level
for a
0dB
indication on the 708 meter in the
L
position.
2. Check the Mod-Monitor reading of Total Peak Modulation. It
should read between 90% and 100%.
3. Also check the Mod-Monitor indication of Pilot Injection Level. If
necessary, adjust the 708
PILOT INJ.
control for a 10% reading.
4. Switch the Mod-Monitor to display left and right channel levels.
The left channel should measure about –1dB. Ideally, the right
channel should read –70dB or below.
5. Adjust the front-panel
MPX EQUAL.
control for best stereo
separation.
6. Change the Audio Generator frequency to 15kHz. Adjust R44 for
best stereo separation at this higher frequency. R44 is located
behind the
COMPOSITE OUTPUT
connector.
7. Repeat steps 5 and 6 to secure greatest separation at 1.5kHz and
15kHz, respectively. These two adjustments interact, but there will
be only one final setting of each which will yield best separation at
the two test frequencies. The optimum adjustment should yield
>65dB separation at all frequencies between 20Hz and 15kHz, left-
into-right and right-into-left.