Orban OPTIMOD-FM 8600Si, Руководство по эксплуатации

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INTRODUCTION ORBAN MODEL 8600Si
Low-pass filters (including anti-aliasing filters in digital links), high-pass filters, trans-
formers, distribution amplifiers, and long transmission lines can all cause the above
criteria to be violated, and must be tested and qualified. It is clear that the above
criteria for optimal control of peak modulation levels are most easily met when the
audio processor directly feeds the stereo encoder. In the 8600Si, no circuit elements
that might distort the shape of the waveform are interposed between the audio
processor and the stereo encoder. We therefore recommend using the 8600Si with
its built-in stereo encoder whenever practical.
Best Location for OPTIMOD-FM
The best location for OPTIMOD-FM is as close as possible to the transmitter, so that
its stereo encoder output can be connected to the transmitter through a circuit path
that introduces the least possible change in the shape of OPTIMOD-FM’s carefully
peak-limited waveform — a short length of coaxial cable. If this is impossible, the
next best arrangement is to feed the 8600Si’s AES3 digital output through an all-
digital, uncompressed path to the transmitter's exciter.
Use the 8600Si’s left and right analog audio outputs in situations where the stereo
encoder and exciter are under the jurisdiction of an independent transmission au-
thority, and where the programming agency’s jurisdiction ends at the interface be-
tween the audio facility and the link connecting the audio facility to the transmitter.
(The link might be telephone/post lines, analog microwave radio, or various types of
digital paths.) This situation is not ideal because artifacts that cannot be controlled
by the audio processor can be introduced by the link to the transmitter, by transmit-
ter peak limiters, or by the external stereo encoder.
If the transmitter is not accessible:
All audio processing must be done at the studio and you must tolerate any damage
that occurs later. If you can obtain a broadband (0-75 kHz) phase-linear link to the
transmitter, and the transmitter authority will accept the delivery of a baseband en-
coded signal, use the 8600Si’s internal stereo encoder at the studio location to feed
the STL. Then feed the output of the STL receiver directly into the transmitter’s ex-
citer with no intervening processing.
If an uncompressed AES3 digital link is available to the transmitter, this is also an ex-
cellent means of transmission, although it will not pass the effects of the 8600Si’s
composite processor (if you are using it). However, if the digital link employs lossy
compression, it will disturb peak levels.
If only an audio link is available, use the 8600Si’s left and right audio outputs and
feed the audio, without pre-emphasis, directly into the link. If possible, request that
any transmitter protection limiters be adjusted for minimum possible action —
OPTIMOD-FM does most of that work. Transmitter protection limiters should re-
spond only to signals caused by faults or by spurious peaks introduced by imperfec-
tions in the link. To ensure maximum quality, all equipment in the signal path after
the studio should be carefully aligned and qualified to meet the appropriate stan-
dards for bandwidth, distortion, group delay and gain stability, and such equipment
should be re-qualified at reasonable intervals. (See
Optimal Control of Peak Modula-
tion Levels on page 1-13).