Orban OPTIMOD-FM 8500S Operating Manual page 76

2-20
INSTALLATION
b) You can use either program material or tone to set the output level (and
thus, the on-air modulation).
• To use tone, press the Y
• To use program material, press the N
B) Set the composite output level.
[Skip this step if you will not be using the composite output(s).]
a) Observe the modulation produced by the 8500S's Composite Output 1 on a
modulation monitor or modulation analyzer. Turn the knob to make the
modulation monitor read 100% modulation (usually ±75 kHz deviation).
If you are using program material, make sure that the program material
is loud enough to produce peaks of frequent recurrence that hit the
8500S's peak limiting system, thereby defining the maximum peak level
that the 8500S will produce. In the U.S., we recommend using 900μs peak
weighting on the peak modulation indicator, as permitted by F.C.C. rules.
This will cause the monitor to ignore very low energy overshoots and will
result in the highest peak modulation permitted by law.
In other countries, use a peak-indicating instrument as specified by the
regulatory authority in your country.
If you are required to obey the multiplex power limits specified by ITU-R
BS412-9, you may seldom see peaks hitting ±75 kHz deviation. In this
case, we advise you to set the output level using the 8500S's reference
100Hz tone.
b) Press the Next button and repeat for C
C) Set the Digital Output #2 level.
a) Press the Next button.
b) [Skip this step if you are not using Digital Output #2.]
Turn the knob to set the desired digital output level corresponding to
100% modulation, in units of dB below full-scale.
The most accurate way to set this control is by observing a modulation
monitor or analyzer connected to your transmitter.
D) Set the Digital Output #1 level.
a) Press the Next button.
b) [Skip this step if you are not using Digital Output #1.]
Turn the knob to set the maximum desired output level in units of dB
below full-scale (dBFS).
The "true peak" limiter at the end of the 8500S's HD processing chain is
oversampled at 256 kHz and will prevent overshoots from exceeding
0.3 dB, even after sample rate conversion or D/A conversion.
To mitigate codec-induced overshoots in HD Radio applications, you may
wish to set the level below 0 dBFS.
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