Orban OPTIMOD-FM 5500 Operation Manual page 69

OPTIMOD-FM DIGITAL
20. Activate the 5500's ITU-R BS412-9 multiplex power controller (optional).
[Skip this step if ITU-R BS412 is not enforced in your country. At the time of this
writing, it is only enforced in certain European countries. If your country does
not enforce ITU-R BS412, set the ITU412-9 control to OFF.]
[If you are planning to use the 5500 in its stand-alone stereo encoder mode,
make sure that the multiplex power controller is turned off until you have fin-
ished setting up the other stereo encoder parameters. Otherwise, it will interfere
with setting output levels.]
A) Navigate to Setup > S
B) Set the multiplex power threshold by holding the ITU412 button down and
turning the knob so that the display indicates 0.0 dB.
If your transmission system introduces overshoot in the signal path after the 5500
(including the transmitter), instead set the multiplex power threshold so that it
equals the amount of peak overshoot (in dB) in the transmission system. If you do
not do this, the 5500's ITU-R BS412 controller will set the average multiplex power
too low.
The easiest way to measure system overshoot is to turn the multiplex power control-
ler off temporarily. Then set the 5500's output level (using its built-in 100Hz refer-
ence tone) so that the transmitter produces 75 kHz deviation. Finally, play program
material with lots of high frequency energy and bass transients (like bright rock mu-
sic with heavy kick drum) and observe the peak deviation produced by the program
material. The overshoot is the amount (in dB) by which the deviation with program
material exceeds 75 kHz deviation.
See the notes on the M
Multiplex Power Controller on page 3-53.
21. Set up modulation reduction to compensate for subcarriers, if needed.
In the United States, F.C.C. Rules permit you to add 0.5% modulation for every
1% increase in subcarrier injection. For example, if your subcarrier injection to-
tals 20%, you can set the total modulation to 110% (82.5 kHz deviation). The
5500 has the ability to reduce audio modulation to compensate for subcarriers.
The advantage of using the modulation reduction function is that the pilot injec-
tion stays constant when the audio modulation is reduced. However, using the
modulation reduction function is slightly inconvenient because it requires pro-
gramming and activating at least one 5500 GPI input. If you have the same sub-
carrier injection at all times, a more convenient alternative is to set the desired
modulation level by using the
injection control until the injection equals 9% modulation.
If you wish to use the modulation reduction function anyway:
A) Navigate to Setup > Next > M
E > Next > ITU412.
TEREO NCODER
control on page 3-35 and ITU-R
P O
PX OWER FFSET
C L
OMPOSITE EVEL
R
ODULATN EDUCTN
control(s). Then turn up the pilot
.
2-21
INSTALLATION