User Manual

LBI-38636S

less populated areas where the phone company has not yet

switched to carrier systems. These lines have a fixed

amount of loss, which varies with frequency, temperature,

from deterioration of splices, and from moisture getting

into the cables. When these cables get old, the phone

company sometimes applies DC current to improve the

joints and lower the line loss. In this case, the line is not

usable for DC control.

Normally, a +10 dBm test tone can be applied to

these lines. These lines do not normally include any type

of voice limiters.

The second type of line is a WIRE LINE WITH

AMPLIFIERS. These lines are normally supplied when

the loss of available lines is too high. An amplifier or

several amplifiers are added to the line to make up for the

loss.

One commonly used amplifier is the E-6 repeater.

This amplifier will pass DC current and they have been

used on DC lines for years. These amplifiers include

limiters, which start limiting at somewhere around 0 dBm

input to the amplifier. The limiters do not cause any real

problems on DC systems since only the voice peaks are

clipped. However, special care must be used when

applying them to tone remote control systems.

Each amplifier can be adjusted for up to 12 dB of

gain. If the loss is more than 12 dB, one or more

amplifiers may be added. The amplifier(s) can be placed

at any point in the line.

The third type of telephone line is a Derived Facility

using carrier equipment. Since this is the most

complicated, more care is required when connecting radio

equipment. This type of line will be available more often

in the future.

The telephone company supplies two wires at each

end of the circuit. Each two-wire end goes to some point

in the circuit where it is converted to a four-wire circuit

and then connected to the carrier equipment. A four-wire

circuit can be ordered if that is what is required. At the

other end, it is taken out of the carrier equipment and

converted back to the two-wire circuit. The carrier

equipment has a transmit path and a receive path. The

gain is adjustable each way.

Figure 6 - T/R Shelf Connections