XRT7295AT

9

Rev.1.20

STS-1 SIGNAL REQUIREMENTS AT THE STSX

For STS-1 operation, the cross-connect is referred at the

STSX-1. Table 4 lists the signal requirements at the

STSX-1. Instead of the DS3 isolated pulse template, an

eye diagram mask is specified for STS-1 operation

(TA-TSY-000253). The XRT7295AT correctly decodes

any transmitted signal that meets the mask shown in

Figure 6

at the STSX-1.

Parameter

Specification

Line Rate

51.84 Mbps

Line Code

Bipolar with three-0 substitution (B3ZS)

Test Load

75W±5%

Power Levels

A wide-band power level measurement

at the STSX-1 interface using a low-pass

filter with a 3dB cutoff frequency of at

least 200MHz is within -2.7 dBm and 4.7

dBm.

Table 4. STSX-1 Interconnection Specification

Figure 6. STSX-1 Isolated Pulse Template for Bellcore TA-TSY-000253

1.0

0.8

0.6

0.4

0.2

0

-1.0

-0.5

0

0.5

1.0

1.5

2.0

Time Slots - Normalized To Peak Location

LINE TERMINATION AND INPUT CAPACITANCE

The recommended receive termination is shown in

Figure 3

The 75 W resistor terminates the coaxial cable

with its characteristic impedance. The 0.01mF capacitor

disturbing the internally generated DC bias level present

typical.

LOSS LIMITS FROM THE DSX-3 TO THE RECEIVE

INPUT

The signal at the cross-connect may travel through a

distribution frame, coaxial cable, connector, splitters, and

back planes before reaching the XRT7295AT device.

This section defines the maximum distribution frame and

cable loss from the cross-connect to the XRT7295AT

input.

The distribution frame jack may introduce 0.6 ±0.55 dB

of loss. This loss may be any combination of flat or

shaped (cable) loss.

The maximum cable distance between the point where

the transmitted signal exits the distribution frame jack and

the XRT7295AT device is 450 ft. (see Figure 2.) The

coaxial cable (Type 728A) used for specifying this

distance limitation has the loss and phase characteristics

shown in Figure 7 and Figure 8. Other cable types also

may be acceptable if distances are scaled to maintain

cable loss equivalent to Type 728A cable loss.

TIMING RECOVERY

External Loop Filter Capacitor

Figure 3

shows the connection to an external 0.1mF

capacitor at the LPF1/LPF2 pins. This capacitor is part of

the PLL filter. A non-polarized, low-leakage capacitor

should be used. A ceramic capacitor with the value 0.1mF

± 20% is acceptable.