Orban OPTIMOD-AM 9300, Руководство по эксплуатации

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INTRODUCTION ORBAN MODEL 9300
frees the system from potential overshoot. (The Orban 6300 can be 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.
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. Moreover, slight frequency response irregularities and non-constant group
delay characteristics will alter the peak-to-average ratio, and will thus reduce the ef-
fectiveness of any peak limiting performed prior to their inputs.
AM Transmitters and Antennas
The behavior of an FM station is more or less determined by the behavior of the ex-
citer. Alas, this is not true in AM broadcast! The performance of an AM broadcast
station is highly dependent upon the high-power sections of the transmitter and
upon the behavior of the antenna system.
The extremely high average power and the pre-emphasized high-frequency compo-
nent of audio processed by OPTIMOD-AM put great demands upon the performance
of the transmitter and antenna system. While improved results can be expected
from most facilities, outstanding results can only be achieved by facilities having
transmitters that can accurately reproduce OPTIMOD-AM's output without changing
the shape of the waveform, and having wide-band, symmetrical antenna arrays.
Any AGCs, compressors, limiters, and clippers that follow OPTIMOD-AM in the circuit
should be bypassed. OPTIMOD-AM provides all of these functions itself.
Bypassing the Transmitter's Internal Filters and Clippers
Some AM transmitters, especially those supplied to stations outside of North or
South America, contain built-in filters and clippers after their audio inputs. The fil-
ters may have various purposes: A low-pass filter is often included to ensure that the
transmitter's output spectrum adheres to the occupied bandwidth specifications of
the governing authority. A high-pass filter may be present to protect the transmitter
from damage. Safety clippers are often present to prevent the modulator from be-
ing over-driven.
As discussed in earlier sections, accurate reproduction of OPTIMOD-AM's output re-
quires that the deviation from linear phase must be less than 10 degrees, 30-9500Hz.
Frequency response must be less than 3dB down at 0.15Hz, and less than 0.1dB
down at 9.5 kHz.