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

75

Ω

RXP

RXN

75

Ω

coax

D02AU1387

RCA Phono

100nF

100nF

STA120

RXP

RXN

100nF

100nF

D98AU986C

STA120