Orban OPTIMOD-FM 8600, Руководство по эксплуатации

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3-76
OPERATION ORBAN MODEL 8600
less of how your facility is configured. It is important to match polarity to avoid a
momentary decrease in loudness during analog/digital receiver crossfades.
This control is best adjusted by observing an HD radio. Using a variable RF attenua-
tor, vary the RF level feeding the radio to force crossfades. If you have correctly ad-
justed the 8600’s
A
NALOG
C
HANNEL
D
ELAY
to time-align the analog and digital chan-
nels, the incorrect setting of the
HD P
OLARITY
control should be clearly audible as a
momentary loudness decrease during the crossfades.
The
HD P
OLARITY
control can make it easier to match the analog and HD channel de-
lay in an HD Radio installation. Temporarily set this control to cause a null, sum the
HD and FM channels, and adjust the
HD D
ELAY
control to achieve the deepest null.
This works best if the HD and FM analog loudnesses are matched; use the
HD L
IMIT
D
R
control to do this.
If your facility has two FM analog exciters. one of which inverts polarity and one of
which does not, you can use the 8600’s
FM P
OLARITY
control to compensate when
switching between transmitters. (See step 13 on page 2-37.) This function can also
be controlled via the 8600’s clock-based automation (see page 3- 42) and by its API
(see step 13 on page 2-55).
Digital Output
You will normally use the AES2 digital output to drive the digital transmitter. How-
ever, you can use any output (
A
NALOG
L/R, AES1
, and
AES2
). The digital outputs
have the following controls, located in the
I
NPUT
/ O
UTPUT
screen.
Out Level (“Digital Output 1” and “Digital Output 2”) sets the digital-channel out-
put level with respect to digital full scale. It is normally set at 0 dBFS, which uses all
the headroom available in the HD transmission channel. To match the loudness of
the analog and digital channels at the receiver, use the
L
IMITER
D
RIVE
control. This
minimizes the amount of peak limiting necessary to match the loudness of the ana-
log and digital channels at the receiver.
When the BS.1770 Safety Limiter is active, it changes the way the
O
UTPUT
L
EVEL
con-
trol operates. See step 10 on page 2-32.
Samp Rate (“Sample Rate”) sets the output sample rate of the digital-channel out-
put to 32, 44.1, 48, 88.2, or 96 kHz.
The 8600’s fundamental sample rate is always 64 kHz, but the internal
sample rate converter sets the rate at the 8600’s digital output. This ad-
justment allows you to ensure compatibility with downstream equipment
requiring a fixed sample rate.
A 32 kHz sample rate cannot represent frequencies higher than approxi-
mately 15 kHz. Therefore, setting the sample rate to 32 kHz automatical-
ly forces the bandwidth to 15 kHz, regardless of the setting of the
HD
B
ANDWIDTH
control
.
Using a 32 kHz sample rate to convey the FM-processed signal will in-
crease peak overshoots because it removes the output spectrum between
14.7 kHz and 17 kHz, some of which is needed to control overshoots. Us-