GAI-Tronics Call/Talk Installation of Call/Talk Systems - Manual (Page 5)

Pub. 42004-251A
Installation of Call/Talk Systems Page: 5 of 9
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Feedback or Distortion on the System
Each page and party circuit must be loaded to the optimum 33 ohms using the line balance assembly. If the
line balance is not connected or is defective, the system will have excessive gain and will break into
feedback quite easily. The voice will also be distorted, and there will be a high level of sidetone in the
handset receiver.
Each party line is terminated with a fixed 33-ohm resistor in the line balance assembly. However, an
adjustable control is provided for the page line to compensate for the number of speaker amplifiers
connected to the system. Improper adjustments will affect gain and will increase the level of sidetone. See
the specific instructions for adjusting the line balance assembly in the Step 5 - Checkout and Adjustment
section.
Very Low Audio Level on One or More Lines at All Stations
It is possible for all or part of the system to function with a dead short across the page or party circuits. If
this occurs, the level of the system will be very low, decreasing to a minimum level in the vicinity of the
short circuit. To locate the short circuit, it is necessary to proceed in the same way as locating a ground
checking junction points with an ohmmeter.
Cross Talk
Cross talk, or inter-channel interference, is generally caused by the accidental crossing of circuits in a
junction box. To check for this condition, measure the resistance between the circuits of the interfering
channels. The resistance should be a very high value or infinite. Leakage or shorts to the ground in two or
more circuits can result in cross talk on those circuits.
In a multi-party line system, it is possible to have a small amount of cross talk between channels if the line
balance resistors are open or not connected. This condition can be detected by the presence of high
sidetone in the handset.
Static Charges
In many normal installations, a static ac voltage may be read from the conductors of the page and party line
circuits to the ground. In many cases, this voltage may be as high as 50 volts or more. This voltage is
induced into the circuits by capacitance to the ac power circuit (generally carried in the same cable and also
from power cables paralleling the communication cables). This voltage is inconsequential and can be
ignored. Only when one side of the page or party circuit becomes grounded are any undesirable effects
produced.
Audio Voltage
In a properly operating system, audio voltage read across any of the page or party circuits (L1 to L2) will
be 0.5 to 0.75 volts ac on peaks when an audio signal is present such as when someone is speaking into a
handset. The voltage will be proportional to the loudness of the person’s voice using the handset.
One Inoperative Station in a Working System
Except for a wiring error, an inoperative station indicates a defect in the amplifier at that station. This is
quickly checked by installing a spare amplifier or exchanging amplifiers with a properly operating station.