Instruction manual

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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.