measuring instrument has a low impedance (i.e., 75
Ω
or 50
Ω
) it is necessary to connect the
instrument to an isolated monitor point in order to prevent the additional load presented by the
low impedance input from affecting the level to be measured.
2.With the measuring instrument properly tuned to the frequency of the channel to be
adjusted, set the IF (subcarrier level) screwdriver adjustment on the front panel for the proper
level for your system.
4-5. Deviation Adjustment (DEV).
The 455 Transmitter is designed to operate with a maximum peak deviation of the subcarrier of
150 kHz (300 kHz peak-to-peak) in the "wide" mode, and 73 kHz (146 kHz peak-to-peak) in
the "narrow" mode. A built-in limiter limits peak subcarrier deviation to approximately 168
kHz in the "wide" mode, and 82 kHz in the "narrow" mode. This deviation is a result of the
entire composite signal consisting of L+R, L-R, pilot, SAP, and PRO channels.
If your stereo generator has a built-in Bessel null calibration tone, it may be used
to accurately set the deviation of the 455 Transmitter in the "narrow" deviation mode. This mode
may be used even if you intend to use the "wide" deviation setting in your application.
Switching from "narrow" to "wide" will maintain the deviation calibration within
approximately one percent.
The inputs on the 455 are designed to accept 2.828V p-p signals for 100% modulation levels.
The deviations assigned to the various inputs are as follows:
Input Deviation Setting
Wide Narrow
Composite........................... ±150.0kHz ±73kHz (L+R, pilot, L-R, SAP, PRO)
Stereo.............................. ±113.0kHz ±55kHz (L+R, pilot, L-R)
SAP.................................. ±30.8kHz ±15kHz
PRO................................... ±6.2kHz ±3kHz
If your BTSC stereo generator can be adjusted to provide the required signal level (2.828V p-
p), it is recommended that the 455 DEV control be left unchanged from the factory setting, and
any adjustments be made at the stereo generator.
455 Operation Manual
Page 28
6/23/98
