Orban OPTIMOD 5750 Operating Manual page 84

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Orban 5750 Technical Manual Operation
The advantage of using the modulation reduction function is that the pilot injection stays constant when the audio
modulation is reduced. However, using the modulation reduction function is slightly inconvenient because it requires
programming and activating at least one 5750 GPI input. If you have the same subcarrier injection at all times, a
more convenient alternative is to set the desired modulation level by using the Composite Level control(s). Then
turn up the pilot injection control until the injection equals 9% modulation.
To comply with FCC Rules, set the modulation reduction to one-half the injection of the associated subcarrier. For
example, if your subcarrier injection totals 20% from two 10% subcarriers, set Modulation Reduction 1 TO "5%" and
Modulation Reduction 2 to 5%. This will reduce your audio modulation to 90% (100% – 5% – 5%). When you add
back the 20% modulation due to the subcarriers, you get the required 110% total modulation.
The Modulation Reduction function is active as long as signal is applied to its associated GPI input.
MULTIPLEX POWER THRESHOLD: Set the MPX Power Threshold control to the target loudness specified by your
country's governing authority.
The BS.1770 safety limiter and meter have been included to allow your OPTIMOD to comply with government
regulations in countries that enforce BS.1770-based loudness control (per EBU Recommendation R 128) in analog
FM transmission. Unless your country requires this, leave the BS.1770 Safety Limiter off.
The analog-chain BS.1770 safety limiter and meter are calibrated with reference to 100% modulation with 50µs
preemphasis (75 kHz deviation) per section 5.9 of EBU Tech 3344 ("Practical guidelines for distribution systems in
accordance with EBU R 128").
The BS.1770 Safety Limiter is usually used in conjunction with the BS.412 Multiplex Power Limiter. The processing
chain is configured as follows:
MPX Offset Control → BS.1770 controller (0 to 3dB GR) → Peak Limiter →
BS.1770 controller (>3dB GR) → BS.412 Controller
SYNC REFERENCE: there are many options to choose from for you piolt sync reference. Default is Internal.