Telegraph relay

Yesterday I posted a photo of a telegraph sounder. It would make loud clicking sounds when receiving a telegraph signal. To ensure a strong and even signal to the sounder a telegraph relay was connected to the incoming line. Office batteries were connected to the relay. The relay would switch the more powerful electricity from the batteries off and on to match the incoming signal. Adjusting screws on the relay could be used to compensate for very weak signals.

Although the sounder produced a fairly loud sound it was useful sometimes to boost the sound level to compensate for external noises such as a typewriter being used to transcribe the message. The sounder was placed in a triangular box, open on one side, and mounted on a moveable arm. The sounder could then be pulled as close to the ear as necessary.

With lots of telegraph traffic destined for other stations the station agent would sometimes switch the sounder off. The relay made just enough sound that the station agent would know to switch the sounder on if the message was for that particular station.

When receiving a morse code message, especially a long one, it was necessary to have a method to alert the sending station if part of the message was misunderstood. Otherwise, the whole message would have to be repeated. Opening up the telegraph line briefly at the receiving station would cause the sounder at the sending station to stop working and the sender would stop transmitting. The receiving station could then send a short code requesting what needed to be repeated.

To send a message one used a "key" which was held between the thumb and forefinger. A quick press down on the key indicated a dot while a slightly longer press indicated a dash. More proficient morse code operators used a "bug". Pressed to the left it created a dash. Pressed and held to the right it produced a series of evenly spaced dots until released. The speed of the dots was adjustable from very slow to very fast. A much higher rate of transmission was attainable using a bug.