Orban OPTIMOD-FM 8600, Руководство по эксплуатации

Страница: 97 / 397

OPTIMOD-FM DIGITAL INSTALLATION
2-37
that the 8600 will produce. In the U.S., we recommend using 900
µ
s 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 implement the average modulation limits specified
by ITU-R 412-7, you may seldom see peaks hitting
±
75 kHz deviation. In
this case, we advise you to set the output level using the 8600’s reference
400Hz tone.
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 totals 20%, you can set the total modulation to 110% (
±
82.5
kHz deviation). This implies that you must set the 8600’s composite out-
put level for the equivalent of 90% modulation, not counting the subcar-
riers. (90% + 20% = 110%.) This will mean that pilot injection will be
about 8% modulation instead of the desired 9%. From the Input/output
> Composite screen, adjust
P
ILOT
L
EVEL
control as necessary to produce
9% modulation (
±
6.75 kHz deviation). This will ordinarily require you to
set the
P
ILOT
L
EVEL
parameter to “10%.”
12. Set preemphasis mode of Output meters (optional).
When the
M
ETER
S
ELECT
switch (in
I
NPUT
/O
UTPUT
> HD D
IGITAL
R
ADIO
) is set to
FMO
UT
L
EVEL
, the 8600’s Output meters normally indicates the peak output level
of the FM analog processing, which is always pre-emphasized. If you wish to ap-
ply de-emphasis before these meters, navigate to
I
NPUT
/O
UTPUT
> U
TILITIES
and set
the
FM O
UTPUT
M
ETER
to
D
E
-E
MPH
.
The default is
P
RE
-E
MP
.
13. Set the polarity of the analog FM processing (optional).
In HD Radio installations, this command is useful when switching the 8600 be-
tween transmitters if the transmitters’ exciters produce opposite FM modulation
polarities when driven by identical digital audio input signals. This setting affects
any output emitting the analog FM processed signal, including the composite
output.
A) Navigate to the
I
NPUT
/
OUTPUT
>
U
TILITES
screen.
B) Set the
FM P
OLARITY
control to
P
OSITIVE
or
N
EGATIVE
as appropriate for your
transmitter.
14. Configure composite outputs.
[Skip this step if you are not using the composite baseband outputs.]
A) Navigate to the
I
NPUT
/
OUTPUT
>
C
OMPOSITE
screen.
B) Adjust the composite level at the composite output(s) you are using so that
the FM carrier is modulated to 100% on modulation peaks. Alternately, you
can use tone.