pro bel Freeway Manual page 9

Pro-Bel Ltd
Technical manual
Digital audio connections
Cable should be of good lIOn design with a foil shield, such as Canford DST. This
shield must make contact all round at the entry to the mating connector body.
Pro-Bel equipment with AES3 interfaces is fitted with '0' type connectors and the
shield is grounded to the chassis at the point of entry. The '0' type shield should
be of the tinned type fitted with screw-locks and with dimples on the male part.
Where a number of channels use the same connector, an overall shield is
preferred in addition to individual shields and this must also be firmly grounded
at both ends .
Serial digital video inputs and outputs
Cable should be good quality 75n design with double braided screens such as
PSFl/3 or Belden 8281. Pro-Bel equipment with Digital Video ('501' or SMPTE
259M) interfaces is fitted with BNC type connectors where the shield is grounded
to chassis at the point of entry. BNC plugs must be of the best quality as this type
is prone to EMC leakage if contact is not good all round the shell.
It is possible to improve the emissions caused by this leakage by using cables with
ferrite collars . This prevents leakage affecting adjacent cables in the installation
space.
Analogue audio (including time-code)
This causes the least problem as the signal spectrum is benign and the circuit
designs generally reject most unwanted signals. Some interference could occur if
the equipment contains processors, etc; so all screens are grounded at the point
of entry. Good quality cables with foil shields should be used with the shield
carried through from end to end, and connected to the chassis earth at the point
of entry using a very short tail.
Analogue video
As with analogue audio the risk lies with processors within the same equipment.
All output BNCs have the shield grounded at the fixing point and most inputs.
However, some inputs have floating connectors for maintenance of common-mode
rejection. Again, only good double-screened cable such as PSFl/3 should be used.
6540T-00 l'Jov 97
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