Magnetic detector

A magnetic detector was part of the wireless apparatus in the radio room of the RMS Titanic which was used to summon help during its famous 15 April 1912 sinking.

[7] Many other wireless researchers such as E. Wilson, C. Tissot, Reginald Fessenden, John Ambrose Fleming, Lee De Forest, J.C. Balsillie, and L. Tieri had subsequently devised detectors based on hysteresis, but none had become widely used due to various drawbacks.

Marconi devised a more effective configuration with a moving iron band driven by a clockwork motor passing by stationary magnets and coils, resulting in a continuous supply of iron that was changing magnetization, and thus continuous sensitivity (Rutherford claimed he had also invented this configuration).

In operation, the band passes over two grooved pulleys rotated by a wind-up clockwork motor.

[1][2] The iron band passes through the center of a glass tube which is close wound with a single layer along several millimeters with number 36 gage silk-covered copper wire.

The radio signal from the antenna (A) is received by a tuner (not shown) and passed through the excitation coil C, the other end of which is connected to ground (E).

The audio pickup coil is connected to a telephone receiver (earphone) (T) which converts the current pulse to sound.

The detector produced electronic noise that was heard in the earphone as a "hissing" or "roaring" sound in the background, somewhat fatiguing to listen to.

Each jerk produced a tiny change in the magnetic field through the coil, and induced a pulse of noise.

The strength of the magnetic field of the permanent magnets at the iron band must be of the same order of magnitude as the strength of the field generated by the radio frequency excitation coil, allowing the radio frequency signal to exceed the threshold hysteresis (coercivity) of the iron.