Orban OPTIMOD-FM 5518, Руководство по эксплуатации

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INTRODUCTION ORBAN MODEL 5518
put, the maximum digital word at the input corresponds to the 0 dB point on the
5518’s input meter.
Composite Output Level
When its left/right overshoot limiter and composite limiter are enabled, the 5518
controls instantaneous, absolute peak levels to a tolerance of approximately

0.1
dB. Composite modulation is indicated in percentage modulation, absolute instan-
taneous peak indicating. 100% is calibrated to the highest composite peak modula-
tion level that the processing will produce and ordinarily corresponds to

75 kHz-
carrier deviation.
Note that if the 5518’s subcarrier inputs are used, the meter will not indicate the
subcarriers’ effect on composite modulation because the subcarriers are mixed into
the composite signal in the analog domain, after it is metered. Therefore, you must
mentally add the subcarriers to the meter indication or refer to an external, cali-
brated modulation monitor.
Built-in Calibrated Line-up Tones
To facilitate matching the output level of the 5518 to the transmission system that it
is driving, the 5518 contains an adjustable test tone oscillator that produces sine
waves at 5518’s (analog or digital) left, right and composite outputs. The frequency
and modulation level of the line-up tones can be adjusted from the front panel (as
described in Section 3).
The stereo encoder is calibrated so that 100% left or right modulation will provide
100% modulation of the stereo composite signal, including pilot tone but excluding
any SCA subcarriers.
The pilot tone stereo system has an interleaving property, which means that the ste-
reo composite modulation is approximately equal to the higher of the left or right
channels. Because the pilot tone is phase-synchronous with the stereo subcarrier, the
composite modulation will actually increase about 2.7% when the modulation is
changed from pure single-channel to L+R modulation while the peak audio level is
held constant.
You can adjust the frequency and modulation level of the built-in line-up tone. You
can use the front panel, the PC Control software, or the opto-isolated remote con-
trol interface ports to activate the Test Tone.
The 5518’s analog outputs are seldom used, but for completeness we
should state that when the 5518’s left/right analog output is switched to
F
LAT
, a deemphasis filter is inserted between output of the 5518’s audio
processing and its line output. Thus, as the frequency of the Test Tone is
changed, the level at the 5518’s line output will follow the selected
deemphasis curve. In most cases, the preemphasis filter in the driven
equipment will undo the effect of the 5518’s internal deemphasis, so the
5518’s output level should be adjusted such that the tone produces 100%
modulation of the transmission link as measured after the link’s preem-
phasis filter. At 100Hz, switching the deemphasis out or in will have neg-
ligible effect on the level appearing at the 5518’s left and right audio
outputs.