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INTRODUCTION
ORBAN MODEL 8382
The Orban 8200ST can be readily configured to produce a pre-
emphasized output.
Further, it is common for a microwave STL to bounce because of a large infrasonic
peak in its frequency response caused by an under-damped automatic frequency
control (AFC) phase-locked loop. This bounce can increase the STL’s peak carrier de-
viation by as much as 2dB, reducing average modulation. Many commercial STLs
have this problem.
Video microwave STLs with audio subcarriers:
Many video microwave STLs provide several audio subcarriers above the video base-
band (typically between about 6 and 8 MHz). Some of these subcarriers have suffi-
cient bandwidth to pass composite stereo, while others are only suited for 50-
15,000Hz audio.
The performance of such audio subcarriers should be qualified in exactly the same
way as composite and dual microwave STLs, respectively. Please refer to the discus-
sions on composite and dual microwave STLs in this section of the manual.
Analog Landline (PTT / Post Office Line)
Analog landline quality is extremely variable, ranging from excellent to poor.
Whether landlines should be used or not depends upon the quality of the lines lo-
cally available, and upon the availability of other alternatives. Due to line equalizer
characteristics and phase shifts, even the best landlines tend to veil audio quality
slightly. They will certainly be the weakest link in a TV broadcast chain.
Slight frequency response irregularities and non-constant group delay characteristics
will alter the peak-to-average ratio, and will thus reduce the effectiveness of any
peak limiting performed prior to their inputs.
STL and Exciter Overshoot
Earlier in this section, we discussed at length what is required to prevent STLs from
overshooting. There are similar requirements for TV exciters. Nevertheless, in some
installations some overshoot is inevitable. If this is a problem in your installation, the
8382’s remote control feature offers the means to reduce the peak level of the
8382’s audio output as necessary. This way, you can still use the 8382’s line-up tone
to adjust the steady-state deviation to
75 kHz. Yet, the reduced peak level of the
audio emitted from the 8382 ensures that the carrier deviates no further than
75
kHz after overshoot. This overshoot reduction can be selected on the Input/output
screen, and the remote operation can be selected in System Setup: Network / Re-
mote.
Note that it is normal for BTSC stereo encoders to introduce a moderate amount of
fast peak overshoot because their input low-pass filters are not overshoot compen-
sated. This does not ordinarily cause any operational problems. Because the output
bandwidth of the 8382 is effectively limited to 16 kHz, these filters are required to
do a minimum amount of work, which minimizes such overshoot.
Summary of Contents for Optimod-TV 8382
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