4-94

MH89761

Advance Information

Applications

The MH89761 can be connected to the MH89760B
as illustrated in Figure 1. All pins on the MH89761
not shown connected in Figure 1 should be left open.
The internal circuit of the equalizer is shown in
Figure 2. The MH89761 has two separate circuits; a
6dB pad and an equalizer.

Ti and Ri are inputs to the 6dB pad on the device.
The outputs of the pad are brought out on TL and
RL. The 6dB pad is provided to loopback the
transmit signal back to the receive without altering
the equalizer settings. The 4 pole double throw relay
shown in Figure 1 permits connection of the output of
the transformer TR1 to either the equalizer or the
fixed 6dB pad. For normal operation and
transmission out to the line, the transformer should
be connected to the equalizer inputs EIT and EIR.
Enabling the relay will switch the connection through
the 6dB pad for loopback diagnostics.

The MH89761 is designed to accept output from the
secondary of the T1 transmit transformer and
condition it for transmission over twisted pair. The
seven switches (S1 to S7) permit configuration of the
equalizer for different line lengths. The pulse
amplitude at the secondary of TR1 is approximately
6V. Passing this signal through the equalizer with
zero line length setting on the switches will result in
attenuation of the pulse by 6dB. This will ensure that
the pulse fits in the template shown in Figure 3 and
meets DSX-1

requirements. By switching in

different C and L components, the frequency and
phase response of the equalizer can be altered as
shown in Figures 4 and 5. Note that the circuit
attenuates lower frequencies more than higher
frequencies. Consequently, when a pulse is passed
through the equalizer, lower frequency components in
the signal are attenuated more than higher frequency
components. The intention is to compensate for the
attenuation properties of twisted pair cable, which
tends to attenuate higher frequencies more than
lower frequencies. The net result is that a pre-
equalized pulse will meet DSX pulse requirements
after traversing a specific length of cable.

The cable length indicated along withthe equalizer
switch settings in Figure 4 are specific to 22 awg
ABAM cable interfaced to an MH89760B equipped
with a Filtran

TFS2573 transformer. Different

equalizer settings may be more appropriate for other
cable and transformer types. Figure 6 shows the
generic switch settings for different levels of
equalization.

Reference:

ANSI T1.102 - 1987, Section 2.2

Manufacturer: Filtran

Ltd.

(613) 226-1626

Figure 2 - 6dB Pad and Equalizer Pin

6dB Pad

4870pF

2150pF

TxT

EiT

EQUALIZER

100

200

100

22µ

200

EiR

TxR

2150pF

4870pF

390

4-95

Advance Information

MH89761

Figure 3 - DSX-1 Line Pulse Template (Reference: ANSI T1.102-1987)

Figure 4 - Typical Frequency Response of the Equalizers

AAAAAAAAA

AAAA

AAA

AAAA

AAA

AAAA

115%
105%

95%
90%
80%

50%

-7%
-5%

-20%

-45%

Nominal

Pulse Shape

SYMBOL

TIME

100 ns

75 ns

175 ns

50 ns

100 ns

75 ns

50 ns

375 ns

150 ns

130 ns

175 ns

Note 1: Template is not to scale

A
T
T
E
N
U
A
T
I
O
N

d
B

100K

200K

500K

1000K

2000K

5000K

10M

20M

50M

100M

Frequency (Hz)

Note: 100

Resistive Load

LONG

MEDIUM

SHORT

Short

0-150'

Medium

150-450'

Long

450-655'

OPEN

Equalizer settings

Note: The equalizer shown here is optimum for 22
gauge ABAM cable and Filtran TFS2573
transformer. The distance settings are approximate
and may vary with cable and transformer type

Attenuation Versus Frequency

AAAA

4-96

MH89761

Advance Information

Figure 5 - Typical Phase Response of the Equalizers

Figure 6 - Switch Settings for Different Levels of Equalization

AAA

100K

200K

500K

1000K

2000K

5000K

10M

20M

50M

100M

Frequency (Hz)

Phase Angle Versus Frequency

LONG

MEDIUM

SHORT

Note: 100

Resistive Load

D
E
G
R
E
E
S

- = SWITCH OPENED
X = SWITCH CLOSED

INCREASING EQUALIZATION

MAX. EQUALIZATION

Long Cables

NO EQUALIZATION

Short Cables

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MH89761

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MH89761