BUILDING A TWO-STATION TELEGRAPH SYSTEM
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This page discusses making a simple two-station telegraph system for practice or for public use and display, using vintage telegraph instruments (keys and sounders) with a modern power source (dry cell batteries).
We begin by showing a typical 1882 telegraph system, and then suggesting a better circuit for today's use. (This is a short line system; it does not use relays or additional batteries in a local circuit at each station.) The original circuit was series-wired like this:
station 1 station 2 ... station n !.......sounder - key............sounder-key.............sounder-key......! ! ! ! ! + - battery battery - + ! ! ! ! ground plate ground plate
The batteries were located at the terminal stations. It used the earth as one side of the circuit. Note the battery (cell) polarity. Each key normally had its circuit closing lever closed, so the circuit was completed and each sounder was pulled in (activated). This circuit is good for two or more stations.
When one operator wanted to send a message, he would open the circuit closer on his key, and send with his key. When finished, he would close the circuit closing lever.
Since the circuit was always drawing current while in the "standby" mode, it used special battery cells (Daniel or gravity cells) that did not run down in that condition.
This circuit could be replicated using a small AC-operated (line voltage) power supply putting out the appropriate voltage, and connecting the ground sides of the end stations with a wire.
For public demonstration and use, especially by young children, the use of dry cell batteries (rather than AC line-voltage components) is recommended. However, dry cell batteries would quickly run down in the above circuit. So, using dry cells, the circuit should be open (no current flowing) until a key is pressed. For two stations, this circuit will work:
station 1 station 2 Wire to other station !----SOUNDER----!...........................!----SOUNDER----! ! ! ! ! + ! ! + BATTERY KEY KEY BATTERY - ! ! - ! ! ! ! !---------------!...........................!---------------! Wire to other station
Each battery consists of two D cells (for 3 ohm sounders), or one 6 volt lantern battery (for 150 ohm sounders). Note the polarity of the batteries. The circuit closing lever of each key (if so equipped) should always be left open, or better, removed.
This circuit has the advantage of using only two wires (other DC circuits require three), and as in the original circuit operates both the sender's and the receiver's sounder when operated. The wires and batteries may be hidden beneath the operating table; the lack of the circuit closers on the keys is the only clue that a modern circuit is used.
This internet page provides useful information on the Morse code, the operation of the sounders, and more: Click here.
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