Orban OPTIMOD-FM 8600Si, Operating Manual

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OPTIMOD-FM DIGITAL INSTALLATION
2-11
synchronize the output sample frequency to the frequency present at the sync. The
connector is a female BNC with the shell grounded to chassis.
To permit daisy-chaining sync signals, the input impedance is greater than 1 K
Ω
. If
the 5500 is the last device driven by the sync coaxial cable, you should terminate it
by using a BNC Tee connector and a 75
Ω
BNC terminator. This will prevent perform-
ance-degrading reflections in the cable. This is required for both wordclock and
AES11id operation.
WARNING: Do not apply an AES3 or AES3id signal to this input. Doing so will even-
tually cause your Optimod to suffer a “communications board error.”
AES3id Ratings Encoder Input
The AES3id Input accepts an AES3 signals on a 75
Ω
BNC connector. It can be used in
conjunction with the second AES3 output to loop through a Nielsen Audio® or simi-
lar ratings encoder having a digital input and output. See
Connecting a Ratings En-
coder on page 2-8.
Grounding
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 wheth-
er it is driven from a balanced or unbalanced source.
•
The 8600Si 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.
•
Whenever coaxial cable is used, shields are automatically grounded at both ends
through the terminating BNC connectors.