to carry the electrical signal, and a receiver to convert the electrical signal back to sound waves.
b. Advantages of Telephone Transmission.
(1) Most of us are familiar with telephone communication since we have used it in our homes for the
greater part of our lives. Therefore we are able to use it with less specialized training than any other
form of electrical communication.
(2) An immediate feedback channel exists to verify acknowledgment of understanding.
(3) Reduced to its operating essential, a telephone system is basically simple.
c. Disadvantages of Telephone Transmission.
(1) Messages sent by telephone are susceptible to inaccuracies. Most of these inaccuracies can be
avoided, or at least minimized, by clear enunciation.
Because of these inaccuracies,
misunderstanding is an ever-present possibility.
(2) It is the least secure of the available methods of information transfer. Almost anyone with a suitable
instrument can monitor the telephone conversation. Even with voice inverters, the security is not
reliable.
(3) There is normally no record of the call and the discussion during the conversation. Thus, future
action is difficult to build on the information transferred, and responsibility for the required action is
therefore not established.
(4) The voice message is easily distorted by equipment or facilities over which the voice message passes.
Noise and interference make the voice difficult to understand at times.
(5) The bandwidth of a telephone voice message is relatively large (normally about 300 to 3,500 hertz
(Hz)). Therefore, the telephone system uses more frequency spectrum than narrowband systems such
as teletypewriter.
d. Facsimile Transmission. Pictures, maps, and written pages can be transmitted by facsimile. The image to
be transmitted is placed on the transmitting unit, where it is scanned by a photoelectric device. The photoelectric
device detects shades of light and dark, and converts them to a varying electric current which is transmitted to the
receiving unit. A pinpoint light in the receiving unit varies in intensity as a result of the varying electrical current,
exposing a light-sensitive paper and thereby reproducing the transmitted image.
e. Advantages of Facsimile Transmission.
(1) For some purposes, photographs and drawings convey far more information in less time than word
descriptions.
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