BSS Audio Prosys PS-8810 Owner's Manual - Manual (Page 33)

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PS-8810
DIGITAL SIGNAL PROCESSOR
As implemented in the BSS PS-8810 the IQ Loop is a 20-mA
current loop operating at a baud rate of 38.4kbps. The IQ Loop
must be unbroken.
The IQ Loop connection can use inexpensive twisted-pair wiring
(shielded or unshielded). Here are some guidelines for twisted-
pair wiring:
•
When interference is a problem, use shielded twisted-pair
wire at least 26 AWG in size. The wire should be of good
quality and should have low capacitance (30 pF/foot or less
is suitable).
The shield serves two purposes:
1
It helps prevent the IQ data signal from transmitting to
nearby audio wiring.
2 It helps prevent outside RF from interfering with the data
signal. However, in most cases interference is not a problem
and, since unshielded wire has lower capacitance, it is a
better choice for typical applications.
• Minimize the total capacitance of an IQ Loop. The total
combined capacitance for a IQ Loop should be less than 30
nF. To calculate this, allow approximately 60 pF for each IQ
component in a loop. This accounts for a slight signal
degradation which occurs as data signals pass through a
component.
• Add an IQ Repeater for very long loops—greater than 1,000
feet (305 m)—or when required by high-capacitance wire.
Although BSS recommends adding a repeater for loops longer
than 1,000 feet, it is sometimes possible to go 2,000 feet (610 m)
or more before a repeater is required. The most significant factor
in determining maximum loop length is wire capacitance. Lower
capacitance will allow longer loops (unshielded wire usually has
lower capacitance).
Outside RF interference is seldom a problem for an IQ Loop
especially if shielded twisted-pair wire is used. However, there
are extreme situations when fibre optic wiring is recommended. For
example, locating a IQ Loop next to an AM radio transmission line
may require fibre optic cabling. An extremely long IQ Loop
distance may also require fibre optic cabling. Contact BSS If fibre
optic cabling is required.
Connections IQ Loop
IQ Loop Wiring