Orban Optimod-TV 8382 Operating Manual Download

Page: 35 / 244

OPTIMOD-TV DIGITAL

INTRODUCTION

1-13

Dual Microwave STLs

Dual microwaves STLs use two separate transmitters and receivers to pass the left
and right channels in discrete form. Dual microwave STLs offer greater noise immu-
nity than composite microwave STLs. However, problems include gain- and phase-
matching of the left and right channels, overloads induced by pre-emphasis, and re-
quirements that the audio applied to the microwave transmitters be processed to
prevent over-modulation of the microwave system.

Lack of transparency in the path will cause overshoot. Unless carefully designed,
dual microwave STLs can introduce non-constant group delay in the audio spectrum,
distorting peak levels when used to pass processed audio. Nevertheless, in a system
using a microwave STL, the 8382 is sometimes located at the studio and any over-
shoots induced by the link are tolerated or removed by the transmitter’s protection
limiter (if any). The 8382 can only be located at the transmitter if the signal-to-noise
ratio of the STL is good enough to pass unprocessed audio. The signal-to-noise ratio
of the STL can be used optimally if an Orban Optimod-PC 1101, Optimod 6300,
8200ST Compressor / Limiter / HF Limiter / Clipper or an 4000 Transmission Limiter
protects the link from overload. Of these, the 1101 and 6300 are currently manufac-
tured as of this writing and are the preferred choices because their AGCs are identi-
cal to the AGC in the 8382.

If the 8382 is located at the transmitter and fed unprocessed audio from a micro-
wave STL, it may be useful to use a companding-type noise reduction system (like
dbx Type 2 or Dolby SR) around the link. This will minimize any audible noise
buildup caused by compression within the 8382.

Some microwave links can be modified such that the deviation from linear phase is
less than +10



from 20 Hz to 15 kHz and frequency response is less than 3 dB down

at 0.15Hz and less than 0.1 dB down at 20 kHz. This specification results in less than
1% overshoot with processed audio. Many such links have been designed to be eas-
ily configured at the factory for composite operation, where an entire stereo base-
band is passed. The requirements for maintaining stereo separation in composite
operation are similar to the requirements for high waveform fidelity with low over-
shoot. Therefore, most links have the potential for excellent waveform fidelity if
they are configured for composite operation (even if a composite TV stereo signal is
not actually being applied to the link).

Nevertheless, in a dual-microwave system, the 8382 is usually located at the main TV
transmitter and is driven by the microwave receivers. One of Orban’s studio level
control systems, such as the 8200ST, protects the microwave transmitters at the stu-
dio from overload. The studio level control system also performs the gain riding
function ordinarily executed by the AGC section of the 8382’s processing and opti-
mize the signal-to-noise ratio obtainable from the dual-microwave link.

If the STL microwave uses pre-emphasis, its input pre-emphasis filter will probably
introduce overshoots that will increase peak modulation without increasing average
modulation. If the studio level control system can produce a pre-emphasized output,
we strongly recommend defeating the microwave STL’s pre-emphasis and perform-
ing pre-emphasis in the studio level control system. This frees the system from po-
tential overshoot.

Orban Optimod-TV 8382, Operating Manual

Search results

Summary of Contents for Optimod-TV 8382

Reviews:

Related manuals for Optimod-TV 8382

Brands by name

Popular brands