Grounding - Orban Optimod-FM 8300 Operating Manual

2-10
INSTALLATION

Grounding

locator drawing. To find the I/O board, see the circuit board locator
drawing on page 6-29. The schematic showing J400 is on page 6-49.
Connect your subcarrier generator(s) to the 8300's subcarrier input(s) with coaxial
cable terminated with BNC connectors.
The subcarrier inputs have greater than 600 load impedance and are
unbalanced. The two SCA inputs have different behaviors. SCA1's sensi-
tivity is variable from 220 mV p-p to >10 V p-p to produce 10% injection,
while SCA2's sensitivity is fixed at 772 mV p-p to produce 10% injection.
VR400 on the I/O board sets SCA1's sensitivity. To access VR400, remove
the top cover according to the instructions in step 1 on page 4-2. To find
VR400, see page 6-46 for the I/O board parts locator drawing.
A special variant of the I/O board is available having an added trimmer
(VR401) to set the gain of SCA2. This variant should be specified at time
of order. Please contact Orban customer service (see page 5-13) for more
information.
You can use the 19K R
reference output will be in-phase (0 DEG) with the pilot tone present in the compos-
ite output or will lead it by 90 degrees (90 DEG). 0 DEG is correct for most installa-
tions. Use 90 DEG only if your RDS/RBDS generator's 19 kHz reference input specifi-
cally requires this phase relationship.
Very often, grounding is approached in a "hit or miss" manner. However, with care
it is possible to wire an audio studio so that it provides maximum protection from
power faults and is free from ground loops (which induce hum and can cause oscilla-
tion).
In an ideal system:

All units in the system should have balanced inputs. In a modern system with
low output impedances and high input impedances, a balanced input will pro-
vide common-mode rejection and prevent ground loops — regardless of
whether it is driven from a balanced or unbalanced source.

The 8300 has balanced inputs. Its subcarrier inputs are unbalanced, but fre-
quency response is rolled off at low frequencies to reject hum.

All equipment circuit grounds must be connected to each other; all equipment
chassis grounds must be connected together.

In a low RF field, cable shields should be connected at one end only — prefera-
bly the source (output) end.

In a high RF field, audio cable shields should be connected to a solid earth
ground at both ends to achieve best shielding against RFI.
control in S to determine whether the 19 kHz pilot
EF ETUP
ORBAN MODEL 8300