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
or just buy one
Creating Your Own Telephone Network
Not only is a telephone a simple device, but the connection between you and the phone company is even simpler. In fact, you can easily create your own intercom system using two telephones, a 9-volt battery (or some other simple power supply) and a 300-ohm resistor that you can get for a dollar at Radio Shack. You can wire it up like this:
Your connection to the phone company consists of two copper wires. Usually they are red and green. The green wire is common, and the red wire supplies your phone with 6 to 12 volts DC at about 30 milliamps. If you think about a simple carbon granule microphone, all it is doing is modulating that current (letting more or less current through depending on how the sound waves compress and relax the granules), and the speaker at the other end “plays” that modulated signal. That’s all there is to it!
The easiest way to wire up a private intercom like this is to go to a hardware or discount store and buy a 100-foot phone cord. Cut it, strip the wires and hook in the battery and resistor as shown. (Most cheap phone cords contain only two wires, but if the one you buy happens to have four, then use the center two.) When two people pick up the phones together, they can talk to each other just fine. This sort of arrangement will work at distances of up to several miles apart.
The only thing your little intercom cannot do is ring the phone to tell the person at the other end to pick up. The “ring” signal is a 90-volt AC wave at 20 hertz (Hz).
If you go back to the days of the manual switchboard, it is easy to understand how the larger phone system works. In the days of the manual switchboard, there was a pair of copper wires running from every house to a central office in the middle of town. The switchboard operator sat in front of a board with one jack for every pair of wires entering the office.
Above each jack was a small light. A large battery supplied current through a resistor to each wire pair (in the same way you saw in the previous section). When someone picked up the handset on his or her telephone, the hook switch would complete the circuit and let current flow through wires between the house and the office. This would light the light bulb above that person’s jack on the switchboard. The operator would connect his/her headset into that jack and ask who the person would like to talk to. The operator would then send a ring signal to the receiving party and wait for the party to pick up the phone. Once the receiving party picked up, the operator would connect the two people together in exactly the same way the simple intercom is connected! It is that simple!