Orban 5950 Technical Manual Technical Data 6-9
ITU-R MULTIPLEX POWER CONTROLLER
The ITU-R recommends that the power in the composite baseband signal (including the pilot tone), integrated over
any 60-second interval, not exceed the power in a sinewave that modulates the FM carrier to r19 kHz (25.3%
modulation). Many European countries are now enforcing this recommendation. (See ITU-R 412 Compliance on
page 3-Error! Bookmark not defined. for more information.)
The BS.1770 Safety Limiter for the analog radio processing chain is located immediately before the MPX power
controller. Normally, both are used simultaneously, but when the target loudness is –23 LUFS, the BS.1770 Safety
Limiter typically produces enough gain reduction to cause the MPX Power Controller to produce no gain reduction.
See step Error! Reference source not found. on page 2-Error! Bookmark not defined. for instructions on setting up
the BS.1770 Safety Limiter.
MPX Power Meter
The 03;
32:(5 meter indicates MPX power according to the ITU-R BS.412 standard. All samples are weighted
equally in a 60-second sliding window.
BS.412 requires limiting the integrated power of the composite signal so that it does not exceed the power in a
sinewave that deviates the FM carrier by ±19 kHz (25.333% modulation with reference to ±75 kHz deviation). The
5950’s MPX POWER meter is therefore calibrated so that it indicates 0 dB when the composite output of the 5950
is a sinewave at 25.333% modulation, which is –11.92615 dB with reference to a sinewave at 100% modulation.
The meter is calibrated with reference to the 5950’s 100% peak modulation level. This calibration is only correct if
the transmitter and/or studio-transmitter link do not add overshoots to program material processed by the 5950.
Such overshoots necessitate turning down the 5950’s output level control after it has been calibrated with tone
using an FM modulation meter and the 5950’s built-in line-up tone oscillator. If the output level is turned down
after a tone calibration, the MPX POWER LEVEL meter will read high compared to the actual on-air MPX power. The
error will be equal to the amount that the 5950’s output level control was turned down.
See Error! Reference source not found. starting on page 1-Error! Bookmark not defined. for a discussion of
overshoots and how they force the average modulation to be reduced to prevent peak overmodulation of the FM
carrier.
Because the 5950 does not digitize subcarriers applied to its subcarrier inputs, the 5950’s 03;
32:(5 meter
(which operates in the DSP domain) cannot indicate the power added by such subcarriers. These usually have
constant power, so it is easy to compensate for them. For example, if an FM subcarrier is injected at 4%
modulation, it adds power that can be calculated with an R.M.S. summation of the subcarrier and the rest of the
composite signal.
Assuming that the subcarrier and composite signal are uncorrelated and that the composite signal is limited so that
its power is equivalent to a sinewave at 25.3% modulation, we calculate their R.M.S. sum as follows:
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