Telegraph Repeater.
An extension of the relay system, adopted for long lines. A repeating
station comprises in general terms duplicate repeating apparatus. One
set is connected for messages in one direction, the other for messages
in the opposite direction. The general operation of a repeating set is
as follows. The signals as received actuate a relay which by its local
circuit actuates a key, which in ordinary practise would be the sounder,
but in the repeater its lever opens and closes a circuit comprising a
battery and a further section of the line.
Repeaters are placed at intervals along the line. Each repeater repeats
the signals received for the next section of line with a new battery. It
represents an operator who would receive and repeat the message, except
that it works automatically.
The Indo-European line from London to Teheran, 3,800 miles long, is
worked directly without any hand retransmission, it being carried out by
five repeaters. This gives an average of over 500 miles for each
repeater.
[Transcriber's note: … 650 miles for each repeater.]
Repeaters introduce retardation, and each repeater involves a reduction
in the rate of working. Yet in many cases they increase the speed of a
line greatly, as its speed is about equal to that of its worst section,
which may be far greater than that of the whole line in one.
Synonym--Translater.
Telegraph Signal.
In the telegraph alphabet, a dot, or dash; the signal or effect produced
by one closing of the circuit. A dash is equal in length to three dots.
The space between signals is equal to one dot; the space between letters
to three dots; and the space between words to six dots.
Telegraph, Single Needle.
A telegraph system in which the code is transmitted by the movements of
a needle shaped index which oscillates to right and left, the left hand
deflection corresponding to dots, the right hand deflection to dashes.
The instruments for sending and receiving are combined into one. The
needles are virtually the indexes of vertical galvanometers. In one form
by a tapper key (see Tapper), in another form by a key worked by a
drop-handle (the drop handle instrument), currents of opposite
directions are sent down the line. These pass through both instruments,
affecting both needles and causing them to swing to right or left, as
the operator moves his key.
As galvanometer needle or actuating needle a soft iron needle is
employed, which is polarized by the proximity of two permanent magnets.
This avoids danger of reversal of polarity from lightning, a trouble
incident to the old system.