SECTION 4 FUNCTIONAL DESCRIPTION

11-5805-451-15

FUNCTIONAL DESCRIPTION

4.1 GENERAL

The Express Orderwire Multidirection Unit is a four-wire conference bridging

device which can be used to connect the Express Orderwire Unit to a maxim urn of

nine points in a common voice-frequency path. It provides all points on the common

voice path with full-duplex, two-way capability, while maintaining isolation between

the transmit and receive paths. A block diagram of the equipment is shown i n

figure 4-1, and a brief functional description is provided in paragraph 4.2.

4.2 FUNCTIONAL DESCRIPTION

The circuit interconnections of the Express Orderwire Multidirection Unit

are accomplished in the four-way, four-wire hybrid or hybrids, while the attenuators

and amplifiers a re used to maintain the proper input and output levels required by the

circuit and the hybrid bridges. The block diagram in figure 4-1 shows representative

levels. With the! input receive level from the multiplex equipment at +7 dBm the out-

put of the hybrid is -8dBm. The pads in the output legs are adjusted to 8dB, giving

a transmit output level to the line of -16dBm. The -8dBm hybrid output is amplified

15 dB to +7dBm if it is to be connected to another hybrid. The output level of the

unit to the express orderwire is -8dBm, and the input from the express orderwire

to the unit is +7dBm.

4.2.1 Four-Way, Four-Wire Hybrid Board

The four-way, four-wire hybrid board, Philco Part No. 368-41964, is a

network of twenty-four 732-ohm resistors arranged in a double cube with four input

ports and four output ports (see figure 4-2). The input and output impedance of the

bridge is 600 ohms. The loss between any input and the three nonassociated outputs

( i . e . , input 1 to outputs 2, 3, and 4) is approximately 15 dB. The loss between any

input and its associated output (i. e., input 1 to output 1) is approximately 80dB.

The loss between any input port and the other input ports is approximately 65 dB.

An examination of figure 4-2 will help in analyzing how this loss differential is

At input port 1 ("A" of figure 4-2) notice that the 15-dB lossoutput

ts are at three adjacent corners "B", "C" and "D"), which are separated from

input by only two resistors. The associated output port No. 1 is at the (opposite

corner "E") of the cube which is separated from input 1 by three parallel

paths of six resistors each. A further loss is obtained by the crossover of resistors