ACCURATE ELECTRONICS INC Practice Section 10401200 Rev A January 2014
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3.06 The bridge may be used in tandem to increase the number of available
ports in a 4wire bridge network. This is done by connecting the input and
output of one port (usually the last) of one bridge to the input and output,
respectively, of one port (usually the first) of another bridge module. Tandem
connection of two (2) Model 10401200 Bridges, for example, provides a
4wire 10way bridge. Tandem applications are generally accommodated in the
lossless mode, as loss in this mode through all input and output port
combinations is constant at 0 dB.
3.07 The limiting factor in the numberof modules that can be used in tandem
is cross-port coupling (crosstalk). The cumulative effect of cross-port
coupling generally limits the number of bridge modules that can be used in
tandem to three or four.
3.08 Because these are active bridges, as opposed to more conventional
resistive bridges, the level and impedance control functions may also be
performed by a pad-transformer module, instead of by more expensive line
amplifiers. One pad/transformer is required for each input and output port
used. If more gain is required at a particular port than can be provided by the
bridge module’s active circuitry, a line amplifier may be used instead of a
pad or pad/transformer module.
3.09 The 10401200 affords a choice of port-to-port insertion loss to permit
interfacing with a variety of facilities and equipment. If a carrier channel or
other standard-level 4-wire interface (+7dB receive, -16dB transmit) is
required, the total 23dB loss option is selected. When lossless bridging is
required, the 0dB option is selected. Option jumpers on each leg permit an
amount of port-to-port insertion loss to be selected: -7.0dB in receive ports
and -16dB in transmit ports, or 0dB.
4. INSTALLATION
Inspection
4.01 The bridge modules should be visually inspected upon arrival in order
to find possible damage incurred during shipment. If damage isnoted, a claim
should immediately be filed with the carrier. If stored, the module should be
visually inspected again prior to installation.
Mounting
4.02 Each module mounts in one position of the Type-10 mounting Shelf.
The module plugs physically and electrically into a 56-pin connector at the
rear of the Type-10 Shelf.
Installer Connections
4.03 Before making any connections to the mounting shelf, make sure that
power is OFF and modules are REMOVED. Modules should be put into place
only AFTER they are properly optioned and after wiring is completed.
4.04 Attempts to troubleshoot the bridge internally is not recommended.
4.05 Figure 4 lists external connections to the module. All connections are
made via wire-wrap at the 56-pin connector at the rear of each module’s
mounting shelf position. Pin numbers are found on the body of the 56-pin
connector. Bridge module pin numbers are found on the printed circuit board,
even numbers on the component side, odd numbers on opposite.
NOTE: External connections are compatible with other manufacturers.
Level Adjustments
4.06 The receive levels are adjusted so that the levels from each port at the
input bridging point are all equal. The input bridging point is accessible at the
front panel RX OUT calibration jack. The receive levels are adjusted using
the front panel RX level controls and the -7dB receive pads located on the
main board. The receive level adjustment range is -4dB to +12dB when the
receive pad is in the 0 (zero) position and -11dB to +5dB when in the -7dB
position.
4.07 Connect a terminated transmission measurement set (TMS) to the RX
OUT calibration jack. Apply a tone separately to each receive port. Adjust
the RX level controls / receive pads as required to achieve equal levels from
each port. The specific value of the bridging level is determined by each
installation. Levels in the range of -10dB to 0dB are acceptable.
4.08 The transmit levels are set to meet the requirements of the equipment
connected at each transmit output port. The transmit levels are adjusted using
the front panel TX level controls and the -16dB transmit pads located on the
main board. The transmit level adjustment range is -6dB to +12dB when the
transmit pad is in the 0 (zero) dB position and -22dB to -4dB when in the -
16dB position.
4.09 Using a TMS inject a tone at the front panel TX IN calibration jack. The
level of the injected tone should be equal to the bridging level used above.
Adjust the TX level control / transmit pads as required to achieve the desired
level at each transmit port.
5. OPTIONS
5.01 Each line CIRCUIT of Model 10401200 contains two push-on jumper
options: one selects the -7 dB RCV PAD (CH1 to CH6 - RCV), and the other
selects the -16 dB XMT PAD (CH1 to CH6 - XMT). Locations of these
jumpers on the module’s printed circuit board are shown in FIGURE 3. These
jumpers are normallyset for the same amount of insertion loss, although they
may be set for different amounts if desired. Set all jumpers to the 0 position
for lossless (0dB insertion loss) bridging or set all jumpers to select 23dB
insertion loss as required for carrier-channel or other standard level (+7/-
16dB) 4-wire interfacing. After jumpers are set, further optioning or
alignment is required. (See Circuit Description 5.0)
Receive Pad Selection
5.02 The receive pad is normally selected when the Model 10401200
interfaces with a 4-wire carrier facility. The normal + 7 dBm receive level
from the carrier facility is attenuated by 7 dB, thus presenting a 0 dBm level
to the bridge.
Transmit Pad Selection
5.03 The XMT PAD is normally selected for carrier applications. The normal
0 dBm output from the bridge is attenuated by 16 dB, thus presenting a
standard - 16 dBm transmit level to the 4-wire carrier facility.
6. CIRCUIT DESCRIPTION
6.01 Model 10401200 provides summing and distribution of six VF or data
channels. This circuit description is intended to familiarize you with the 4-
wire 6-way Active Bridge modules for engineering and application purposes
only. Troubleshooting procedures should be limited to those prescribed in
Section 8 of this Practice. Please refer to the block diagrams, Figure 2 as an
aid in following the circuit description.
6.02 The Active Bridge circuitry is identical for each port of the bridge. This
circuitry consists of five-input summing circuit and, for each port output, an
integrated-circuit operational amplifier (op amp). The summing circuit
provides balanced 600 ohm terminating impedance for each input port. For a
particular output port, the summing circuit adds the transmission energyfrom
all other input ports (ie. all input ports except the one with the same number
as the output port) at a low-impedance summing point. The low impedance
of this summing point provides input port isolation.
6.03 The op amp provides switch-controlled gain to overcome the loss of the
summing circuit, and the 10401200 has six such networks.
6.04 References to transmit and receive are with respect to the bridge. All
transmit line and receive line circuits for each port are identical; therefore,
circuit description is based on RX Port 1 and TX Port 1.
6.05 Data or VF signals enter the Bridge on the RX Port 1 tip and ring leads
and are transformer-coupled (via T1) to the input of operational amplifier U-
1. A -7dB RX PAD can be selected to provide the proper level for 4-wire
carrier applications. The front-panel-mounted RX 1 LEVEL potentiometer,
connected in the feedback loop of U-1, provides a level of adjustment of -4
dB to + 12 dB. This is used to compensate for losses in the receive line. The
output of U-1 is coupled to the operational amplifiers associated with transmit
lines 2, 3, 4, 5, and 6 thru a summing network. Thus, all signals present at the
RX LINE 1 input appear at the TX LINE outputs of ports 2,3,4,5 and 6 but
not at the TX port of channel 1.
