Orban OPTIMOD-FM 5700i, Руководство по эксплуатации

Страница: 37 / 335

OPTIMOD-FM DIGITAL INTRODUCTION
1-11
Subcarriers
The stereo encoder has two unbalanced 60
0Ω
subcarrier (SCA) inputs with rear-
panel BNC connectors to accept any subcarrier at or above 23 kHz. The subcarriers
are mixed into each composite output and their level is not affected by the compos-
ite level control for that output. The 5700i does not digitize subcarriers; the mixing
occurs after D/A conversion and is analog.
Subcarrier inputs sum into the composite baseband outputs. Rear-panel accessible
PC-board-mounted trim pots allow the user to adjust the sensitivities of the two SCA
inputs from <100 mV p-p to >10 V p-p to produce 10% injection with respect to
100% modulation = 4 V p-p at the 5700i’s composite outputs (the factory setting is 4
V p-p to produce 10% injection). Thus both inputs accommodate subcarrier genera-
tors with output levels as low as 100 mV p-p.
The correct peak level of the stereo program applied to the stereo encoder some-
times depends on the number of subcarriers in use. Some regulatory authorities re-
quire that total baseband peak modulation be maintained within specified limits.
The 5700i’s remote control feature allows you to reduce the stereo main level by
connecting an on/off signal from your subcarrier generator (See page 2-7). You de-
fine the amount of reduction in percent using the procedure in step 2 on page 2-23.
See page 2-43 for information on programming the remote control.
A jumper (J6) on the circuit board can reconfigure the SCA 2 input to provide the
stereo pilot tone only, which can provide a pilot reference for an RDS subcarrier
generator.
Remote Control Interface
The Remote Control Interface is a set of eight optically-isolated GPI inputs on a DB-
25 connector, which can be activated by 5-12V DC. They can control various func-
tions of the 5700i:
•
Recall any Factory Preset, User Preset, Test Mode state (Bypass or Tone), or exit
from a Test Mode to the previous processing preset.
•
Switch the stereo encoder to stereo, mono from left, mono from right, or mono
from sum audio input. This also determines the feed to the entire processing
chain so that facilities that do not use the 5700i’s stereo encoder can change ste-
reo/mono mode and select the source when in mono mode.
•
Switch the 5700i to use either the analog input or the digital input.
•
Mute any output configured to emit the low-delay monitor signal.
•
Independently activate and defeat the diversity delay applied to the analog, digi-
tal, and composite outputs.
•
Reduce the stereo main and subchannel modulation to compensate for transmit-
ter overshoot and subcarrier inputs (SCAs).