Orban OPTIMOD-FM 5500 Operation Manual page 57

OPTIMOD-FM DIGITAL
example, by connecting the 5500's and exciter's power cords to adjacent
sockets on an AC power strip). If you encounter intractable ground loop
or other noise problems between the 5500 and your exciter, we suggest
purchasing the Orban CIT25 Composite Isolation Transformer. Designed
to be installed adjacent to each exciter, the CIT25 provides rigorous
ground loop isolation between the 5500 composite output and the ex-
citer's input and presents the 5500 with a balanced, floating load. If the
CIT25 is used, the exciter must present a 1k or greater load to the
transformer for proper transformer operation.
Even when its composite limiter is being used heavily, the 5500 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 subcarrier (SCA) 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 5500's composite output in the
analog domain, after D/A conversion of the 5500 stereo encoder's out-
put. 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 5500's composite outputs. (The factory setting is 4 V p-p to pro-
duce 10% injection.)
As shipped from the factory, the second SCA connector emits a stereo pilot tone
reference for RDS or RBDS subcarrier generators. If you wish to reconfigure it to ac-
cept an SCA signal, move the link on jumper J6 (on the Composite/SCA daughter-
board) from pins 3 and 4 to pins 1 and 2.
To access J6, remove the 5500's top cover according to the instructions in
step 1 on page 4-2. The schematic showing J6 is on page 6-38.
Connect your subcarrier generator(s) to the 5500's subcarrier input(s) with coaxial
cable terminated with BNC connectors.
The subcarrier inputs have greater than 600 load impedance and are
unbalanced. The sensitivity of both inputs is user-adjustable 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 5500's composite outputs. (The factory set-
ting is 4 V p-p to produce 10% injection.)
VR1 and VR2 on the Composite/SCA daughterboard set the sensitivity of
SCA1 IN and SCA2 IN respectively and are accessible on the rear panel.
You can use the 19K R
erence output will be in-phase (0 DEG) with the pilot tone present in the composite
output or will lead it by 90 degrees (90 DEG). 0 DEG is correct for most installations.
Use 90 DEG only if your RDS/RBDS generator's 19 kHz reference input specifically re-
quires this phase relationship.
control in Setup to determine whether the 19 kHz pilot ref-
EF
2-9
INSTALLATION