Modulate the sub carrier 100% (+/-50 KHz) with 50 Hz. Measure signal level at
U6 (7). Adjust VR131 for + 10 dBm output. Switch the modulating frequency to 15
KHz, verify that sub carrier deviation r/- 50 KHz. Adjust VR133 for +10 dBm
output from U6. Verify that the circuit is functional by switching the modulating
frequency to 2 KHz at 10% sub carrier deviation (+/-5 KHz), The output of U6 should
drop to -21 dBm (a 31 dB drop from 100% modulation).
AUDIO OUTPUT LEVEL AND BALANCE:
There are two output adjustments. The first is to balance the tip and ring (T&R)
levels, the second is to set the output level to a standard, gen10 dBm into a
balanced 600 Ohm load at 100% modulation.
A convenient way to balance the T&R levels is to connect two precision 1%
300 Ohm resistors in series to make a center tapped 600 Ohm lead. Modulate the
subcarrier 100% with 1 KHz. Monitor the signal level at the junction of the two load
resistors and adjust VR156 for the best null. Check levels at T&R, then should be
identical. Connecting either T or R to ground should increase the level of the
opposite terminal by 6 dB +/- 1 dB. Connecting the center tap of the load to ground
should have no effect on the level.
APPENDIX
B
PMS610 MAINFRAME AND POWER SUPPLY INSTRUCTIONS
The PMS610 is a mainframe power supply for mounting FM SYSTEMS 600
series equipment. Up to three circuit board modules may be accommodated. These
600 series modules may be readily installed in the field with common hand tools, no
soldering is required.
MOUNTING AND SIZE:
Fits Standard 19” wide rack. 1-¾” H x 10-¼” D.
CAPACITY:
Up to three FM SYSTEMS 600 series modules.
POWER:
105-125 VAC 50/60 Hz 0.4 A input, 3 way Plug.
CONNECTORS:
Through-hole
access on the rear panel.
WEIGHT:
4 lbs. minimum, 9 lbs. fully loaded.
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