Getting Started
3-20
3.5.7 Analog backplane cable construction
The analog backplane of the Model 708A Switching System
has two expansion connections (see Figure 3-14). Each con-
nection is part of a printed circuit board with wire traces
0.100 inches apart. Use these connections to expand Model
708A rows to the rows of other Model 708A Switching Sys-
tems. The 20-pin connection is used for expansion of coaxial
matrix cards [does not apply to the Model 7077 (50 pin) or
the Model 7173-50 (no automatic expansion)]. The 50-pin
connection is used for expansion of general purpose cards.
Table 3-6 contains the model numbers of all cards supported
by the Model 708A and also describes the appropriate meth-
od of expansion.
NOTE
Analog backplane expansion does not ex-
pand control of separate Model 708A
Switching Systems as a master/slave sys-
tem. This is accomplished through control
expansion (paragraph 3.5.4).
Recommended cable parts (or equivalent)
NOTE
The 20-pin cable does not maintain the
50
Ω
characteristic impedance of the ana-
log backplane (the 20-pin cable is intend-
ed for DC expansion).
Note: The following cables are available from 3M Corpora-
tion.
20-pin cable
3365/20 (3M)
— 28 AWG ribbon cable rated at >200VDC.
3461-001 (3M)
— 0.1 inch card-edge connector with a cur-
rent rating of 1A > 200VDC (one connector required for
each Model 708A).
3448-54 (3M)
— Strain relief (one strain relief required for
each Model 708A).
50-pin cable
3365/50 (3M)
— 28 AWG ribbon cable rated at >200VDC.
3415-0001 (3M)
— 0.1 inch card-edge connector with a cur-
rent rating of 1A > 200VDC (one connector required for
each Model 708A).
3448-54 (3M)
— Strain relief (one strain relief required for
each Model 708A).
NOTE
The number of connectors/strain reliefs
used in the cable will depend on the num-
ber of Model 708A Switching Systems to
be connected through the backplane.
Specifications exclude errors resulting
from the cable.
When manufacturing the cable:
• Keep the cable length as short as possible. Make sure
adequate length is provided to span the distances be-
tween the Model 708A Switching Systems. If the Mod-
el 708A Switching Systems are not rack mounted,
provide extra clearance if physical layout of the main-
frames is subject to change.
• Make sure adequate cable is allowed between each con-
nector placed on the cable.
• Make sure pin 1 of each connector is aligned for pin 1
on each Model 708A connection. The connectors/con-
nections are not keyed.
3.5.8 Sample expanded matrices
Figures 3-15 through 3-18 contain sample expanded matrix
systems. Use these samples as a guide when designing a ma-
trix system. Refer to paragraph 3.4 for instruments and DUT
considerations while designing a matrix system.
Figure 3-14
Analog backplane expansion connectors
50 Pin Connector
20 Pin Connector
1
1
Analog Backplane
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