Field telephones are one of the best and simplest systems of communication in a base of operations.
communication is Key to early warning and defense strategy.
Field Telephones are best used as a point to point communication solution or a simple “jack plug” switch board can be made with a little skill and then a person to man the switch board – if you require a system with more then 2 points..
They were extensivly used during both world wars and in Vietnam for secure communication.
I am not going to detail exactly how one would create the field telephone — but lets just say its not exactly difficult, the detail i will give is that on microphone and one speaker must obviously be at each end ( plans for making these yourself below although store bought is probably better if you build these before you need them )
I have included a basic circut diagram above I just drew up quickly, this will be what a single phone looks like – that plugs into a switch board, to have a simple phone that only have 2 ends then replace the jack plug with another bell, switch, mic and speaker.
__The Switch Board__
a simple switch board can be made by a few jack plug sockets, low voltage bulbs or leds, and jack plugs , the concept is for each “extention” you need a socket to plug the long line that goes to the phone into – another socket to plug another phone into wired in parallel and an led to indicate that its active, a third socket can be added in parallel to allow an operator to “listen in”, and a Lead with a plug on, this lead will plug into to other sockets to connect phones to others , each phone needs each of these i mentioned, it is best to make the sockets for each in a numbered column
so that you can keep track of the cables.
2 cores wire carries the signal ….. and all the components are in series with a battery ( or dc power source) to form a closed circuit
a simple bell or buzzer can be used ( bells are easy to make out of old relays or hand wound electric coils)
If set up over long distances you could even follow the modernmechanix idea of a simple fax machine , replacing the syncronising belt that provides the drum timing with a clock linked to the second hand and start at exactly the same time Link to plans