Orban OPTIMOD-FM 8700, Operating Manual

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2-10
INSTALLATION ORBAN MODEL 8700i
citer end. This also eases thermal stresses on the output amplifier in the
stereo encoder and can thus extend equipment life.
If a composite isolation transformer is used to break a ground loop, the
exciter
must present a 1k

or greater load to the transformer for proper
transformer operation. See page 1-15.
Even when its composite limiter is being used heavily, the 8700i will al-
ways protect the stereo pilot tone by at least 60 dB (

250Hz from 19 kHz)
and will protect the region from 55 kHz to 100 kHz by at least 75 dB (re
100% modulation). See Figure 5-1 on page 5-4.
The analog subcarrier inputs are provided for convenience in summing subcarriers
into the baseband prior to their presentation to the FM exciter.
The subcarrier inputs will accept any subcarrier (or combinations of sub-
carriers) above 23 kHz. Below 5 kHz, sensitivity rolls off at 6 dB/octave to
suppress hum that might otherwise be introduced into the subcarrier in-
puts, which are unbalanced.
The subcarrier inputs are mixed into the 8700i’s composite output in the
analog domain, after D/A conversion of the 8700i stereo encoder’s out-
put but before the digitally controlled attenuators that set the composite
output levels.
As shipped from the factory, the second SCA connector emits a stereo pilot tone ref-
erence for external RDS or RBDS subcarrier generators. If you wish to reconfigure it
to accept an SCA signal, move the link on jumper J400 (on the I/O board) from pins 3
and 4 to pins 1 and 2.
To access J400, remove the 8700i’s top cover according to the instructions
in step 1 on page 4-2. To find J400, see page 6-51 for the I/O board parts
locator drawing. To find the I/O board, see the circuit board locator
Figure 2-3: Separation vs. load capacitance