Olson Technology LCM-550x1 - Manual (Page 10)

025-000329 REV C Page 10
4.) REAR PANEL
The rear panel of each module has its audio and video inputs and its RF output. The audio and video inputs are RCA
type phono jacks and the RF output is a type “F”.
5.) VIDEO MODULATION ADJUSTMENT (Each modulator).
LCM-550X12 modulator modules are preset at the factory for 85% depth of modulation with a 1V P-P pulse and bar
test signal. If the video modulation needs to be adjusted, follow the procedure below.
Connect the video source (to be used at approximately 1V P-P) to the video input phono jack. The video should be of a
reasonably bright scene (commercials are usually excellent).
Adjust the video modulation control on the front panel to obtain approximately 85% depth-of modulation as measured
on a spectrum analyzer or other test equipment capable of this measurement.
If the video modulation control needs to be set and there is no test equipment available, it can be set fairly close by
comparison. View a video signal on a properly adjusted television receiver or receiver/monitor. Apply the same signal
if possible, or one of equivalent brightness and contrast to the modulator that needs to be set. View the output of this
modulator on the same receiver and adjust the video modulation control for brightness and contrast equivalent to the
directly viewed picture. Use caution and do not set this control too high.
6.) AUDIO MODULATION ADJUSTMENT (Each modulator).
Connect the audio source (to be used at approximately 500mV P-P) to the audio input phono jack.
Monitor the audio on a television receiver and adjust the audio modulation control for proper loudness as compared
with some channel known to be modulating at the correct level (such as a broadcast station).
The two sources of audio should be very similar in their content and should be near maximum loudness as compared to
the average level of their program. In other words, compare a loud passage with a loud passage and set the audio
modulation control with this program material. Use caution and do not set this control too high.
7.) OPERATION WITH COMPOSITE BASEBAND BTSC AUDIO INPUT (Each modulator).
The LCM-550X12 modulators are compatible with a composite baseband BTSC audio input. An internal jumper must
be changed to remove audio pre-emphasis as required for this application.
To remove audio pre-emphasis, disconnect and remove the LCM-550 module from the main shelf and remove its left
side cover. Cut board where indicated.
Replace the module cover, replace the module in the main shelf, and set-up the audio deviation per the instructions for
the BTSC generator being used.
8.) RF OUTPUT AND AURAL CARRIER LEVEL ADJUSTMENT (Each modulator).
A) Using a field strength meter or spectrum analyzer, set the video carrier to the desired level with the output level
(RF) control (typically +40 to +45dBmV).
B) Tune the field strength meter to the aural carrier, which is located 4.5 MHz above the video carrier.
C) Adjust the aural carrier level control (A\V) to the desired level, typically 15dB below the video carrier.
CAUTION: Reducing the aural \ visual carrier ratio to less than 15dB can result in high out-of-band spurious
signals on adjacent channels.