American Contactor BC 608
Although a contactor is often explained as a kind of IFF device in several publications on internet, this is not true. A contactor, even if it is British or American, is actually a device for determining the position of an aircraft. It has nothing to do with identifying if an aircraft is a “friend” or “enemy”. (IFF).
This signal was also called “PIP-SQUEAK” signal.
It is a mechanical clock device with an electrical contact, which switches on a communication transmitter for 14 seconds every minute at a special frequency channel. The direction finder stations home determine then by a cross sense the position of the aircraft.
This contactor is often used in the SCR 522 VHF transmitter/receiver.
The British types are used in fighterpanes, like spitfire, hurricane. A big part of the south-west coast of the British empire was divided in sectors. Each sector had his own airfields with fighterplanes. When a german attack was expected , radar (home chain) determined the location and direction of the ennemy planes. A certain sector was activated then. The fighterplanes of that sector went in the air to be lead to the ennemy. The direction finder stations of that sector (about 2 of them) could determine the position of their fighters by the “Pip-Squeak” signal caused by the contactor transmitter switch on. So by radio contact the could give eventually coarse corrections etc.
This picture above is a contactor, type BC 608: an American product. There have also been British types manufactured, for use in fighter planes.
- The switch on the left is used to activate or deactive the so called PIP-SQUEAK signal.
- The switch on the right is used to activate or deactivate the clockwork of the BC 608.
- The knob in the middle is to rewind the clockwork.
- The quarter section as seen in the upper right in the display represents the 14 seconds read-off timer.
British version PIP-SQUEAK.
The purpose is the same as that one mentioned before. It has been used a lot in the BATTLE of BRITAIN during WW2. The contactor was switching on the transmitter , at a special frequency being not a communication channel, during equal intervals for some seconds. So the monitoring control centres knew exactly the position of the fighter planes by piling them up. If known, they directed the fighters to the locations of the ennemy bombers on their way to Britain, by another radio channel. The locations of the ennemy bombers were detected by the HOME CHAIN radar stations along the coast line.
Pip squeak was an very effective way, leading the fighters to their targets.
Here the Brittisch version of the contactor, mentioned before. It’s a type no 4. Cover of the right box has been removed.
Left the remote contactor, which switches on the transmitter, often a TR9- D used in fighterplanes like the Spitfire.
At the right the maincontactor. It is a mechanical clock, which steps forward the internal remote contactor relay. Can be seen by moving of the needle on the front. In the mechanical clock assembly, there is a heaterelement installed for maximum stability. In the middle of it a key, for winding up the clock.
On the front of the remote contactor, there is that red part, which stands for 14 seconds. The whole scale is 1 minute. So the transmitter is switched on every 14 seconds of 1 minute.
I have tested it on a seperate transmitter, and it workes very well.
The remote contactor has been place on the right of the pilot seat, the master is placed behind the pilot seat.
On the picture above, the same. Only the cover has been replaced. This has to be done because of the temparature stabilisation internally, which was for my test not important..