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