Analog Landline (Ptt / Post Office Line); Using The Orban 8100Ast (Or 8100A/St) External Agc With The 8300; Stl And Exciter Overshoot - Orban Optimod-FM 8300 Operating Manual

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INTRODUCTION

Analog Landline (PTT / Post Office Line)

Using the Orban 8100AST (or 8100A/ST) External AGC

STL and Exciter Overshoot

control (AFC) phase-locked loop. This bounce can increase the STL's peak carrier de-
viation by as much as 2 dB, reducing average modulation. Many commercial STLs
have this problem.
Some consultants presently offer modifications to minimize or eliminate this prob-
lem. If your exciter or STL has this problem, you may contact Orban Customer Service
for the latest information on such services.
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 FM 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.
with the 8300
If you have an OPTIMOD-FM 8100A1 (or 8100A or 8100A/1) installation that uses an
Orban 8100AST (or 8100A/ST) external AGC at the studio to protect an STL (with the
main 8100A, 8100A1 or 8100A/1 chassis at the transmitter), you may wish to con-
tinue to use the external AGC to protect the STL when you install the 8300 at the
transmitter.
If you are keeping your analog OPTIMOD-FM as a standby processor, you will proba-
bly want to use the external AGC to drive both the 8300 and the 8100A1 (also called
8100A/1) transmitter chassis in parallel. This is usually practical. However, complica-
tions will occur if you are not using an Orban 8100AXT2 (also called 8100A/XT2) Six-
Band Limiter Accessory with your 8100A1, because, to correctly drive an 8300, the
external AGC must be strapped as if it were driving an 8100A1 (or 8100A/1) +
8100AXT2 (or 8100A/XT2) system. Therefore, if you have only an 8100A1 (or
8100A/1), you will have to re-strap the external AGC for operation without the XT2
before you can put the standby 8100A1 (or 8100A/1) on the air.
Earlier in this section, we discussed at length what is required to prevent STLs from
overshooting. There are similar requirements for FM exciters. Nevertheless, in some
installations some overshoot is inevitable. If this is a problem in your installation, the
8300's remote control feature offers the means to reduce the peak level of the
8300's audio output as necessary. This way, you can still use the 8300's line-up tone
to adjust the steady-state deviation to 75 kHz. Yet, the reduced peak level of the
audio emitted from the 8300 ensures that the carrier deviates no further than 75
kHz after overshoot. This overshoot reduction can be selected on the input/output
ORBAN MODEL 8300