magnetization "flips" is stationary with respect to the pickup coil, so there is no flux change and no voltage is induced in the pickup coil. 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 rapidly reversing magnetic field from the coil exceeds the coercivity Hc and cancels the hysteresis of the iron, causing the magnetization change to suddenly move up the wire to the center, between the magnets, where the field reverses. This had an effect similar to thrusting a magnet into the coil, causing the magnetic flux through the pickup coil D to change, inducing a current pulse in the pickup coil. The audio pickup coil is connected to a telephone receiver (earphone) (T) which converts the current pulse to sound. The radio signal from a spark gap transmitter consisted of pulses of radio waves (damped waves) which repeated at an audio rate, around several hundred per second. Each pulse of radio waves produced a pulse of current in the earphone, so the signal sounded like a musical tone or buzz in the earphone. Technical details The iron band was turned by a mainspring and clockwork mechanism inside the case. Differing values have been given for the speed of the band, from 1.6 to 7.5 cm per second; the device could probably function over a wide range of band speeds. The operator had to keep the mainspring wound up, using a crank on the side. Operators would sometimes forget to wind it, so the band would stop turning and the detector stop working, sometimes in the middle of a radio message. 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. This was Barkhausen noise due to the Barkhausen effect in the iron. As the magnetic field in a given area of the iron wire changed as it moved through the detector, the microscopic domain walls between magnetic domains in the iron moved in a series of jerks, as they got hung up on defects in the iron crystal lattice, then pulled free. Each jerk produced a tiny change in the magnetic field through the coil, and induced a pulse of noise. Because the output was an audio alternating current and