13/15
STA120
Grounding the shield of the cables a tricky issue. In the configuration of systems, it is important to avoid
ground loops and DC current flowing down the shield of the cable that could results when boxes with dif-
ferent ground potentials are connected.
Generally, it is good practice to ground the shield to the chassis of the transmitting unit, and connect the
shield through a capacitor to chassis ground at the receiver. However, in some cases it is advantageous
to have the ground of two boxes help to the same potential, and the cable shield might be depended upon
to make that electrical connection.
Generally, it may be a good idea to provide the option of grounding or capacitively coupling to ground with
a "ground-lift" circuit.
Consumer Interface
In the case of the consumer interface, the standards call for an unbalanced circuit having a receiver im-
pedance of 75
Ω
±5%. The connector for the consumer interface is an RCA phono plug (fixed socket de-
scribed in Table IV of IEC268-11). The receiver circuit for the consumer interface is shown in Figure 9.
Figure 9. Consumer Input Circuit
TTL/CMOS Levels
The circuit shown in Figure 10 may be used when external RS422 receivers or TTL/CMOS logic drive the
STA120 receiver section.
Figure 10. TTL/CMOS Interface
75Ω
RXP
RXN
75Ω
coax
D02AU1387
RCA Phono
100nF
100nF
STA120
RXP
RXN
100nF
100nF
D98AU986C
STA120
