OPTIMOD-FM DIGITAL
INSTALLATION
2-23
1.
Activate the 5700i’s ITU-R BS412-9 multiplex power controller (op-
tional).
[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 5700i 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
TEREO
E
NCODER
>
Next
>
ITU412.
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 5700i (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 5700i’s ITU-R BS412 con-
troller will set the average multiplex power too low.
The easiest way to measure system overshoot is to turn the multiplex
power controller off temporarily. Then set the 5700i’s output level (using
its built-in 100Hz reference 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 music 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
PX
P
OWER
O
FFSET
control on page 3-43 and
2.
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
5700i 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 5700i 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
C
OMPOSITE
L
EVEL
control(s). Then turn up the pilot
injection control until the injection equals 9% modulation.
If you wish to use the modulation reduction function anyway:
A)
Navigate to
Setup
>
Next
>
M
ODULATN
R
EDUCTN
.
Содержание OPTIMOD-FM 5700i
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