Orban OPTIMOD-FM 8700, Operating Manual

Page: 41 / 390

OPTIMOD-FM DIGITAL INTRODUCTION
1-11
(100ft / 30m of RG-59 / U cable) before any significant audible performance degra-
dation occurs (see the footnote on page 1-15 and refer to
Figure 2-3: Separation vs.
load capacitance on page 2-10). Independent level control of each output is via
software in the I
NPUT
/
OUTPUT
> C
OMPOSITE
screen.
Digital Composite Output
The 8700i provides an AES3 digital composite output at 192 kHz sample rate. Its
output level is set in the Input/Output 5 screen titled Composite 2. At the PC remote,
it is located in the
I/O S
ETUP
S
CREEN
with the tab
D
IGITAL
E
NCODER
.
This output appears on a male XLR-type connector on the rear panel. This output is
fully compatible with and interoperable with the de-facto industry standard digital
connection being implemented by transmitter manufacturers and others.
Subcarriers
The stereo encoder has two unbalanced 60

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 composite
level control for that output.
The 8700i does not digitize subcarriers appearing at these two inputs; the mixing oc-
curs after D/A conversion and is analog.
Subcarrier inputs sum into the composite baseband outputs before the digitally con-
trolled composite attenuators. The sensitivity of the both SCA inputs are variable
from 220 mV p-p to >10 V p-p to produce 10% injection. Internal PC-board-mounted
trim pots determine the sensitivity.
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 the total baseband peak modulation to be maintained within specified limits.
Thus, the level of the stereo main and subchannel must be reduced when a subcarri-
er is turned on. The 8700i’s remote control feature allows you to reduce the stereo
main and subchannel level by connecting an on/off signal from your subcarrier gen-
erator (See page 2-9). You define the amount of reduction (in units of percent mod-
ulation) on the Input/output screen (See page 2-30). See page 2-61 for information
on programming the remote control.
A jumper 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.
Digitized Subcarrier Inputs
Two additional subcarrier inputs are provided on the rear panel. These are digitized
and are summed only into the digital composite output.
Their mix level is set in the Input/Output 5 screen titled Composite 2. At the PC re-
mote, they are located in the
I/O S
ETUP
S
CREEN
with the tab D
IGITAL
E
NCODER
.