Marconi detektorvastuvõtja 106C aastast 1917 (kristalldetektor on näha alumise keskmise ja parempoolse nupu vahel) Aparaat oli ette nähtud morsekoodis signaalide kaugvastuvõtuks (üle ookeani); laineala 200‒3500
English: Marconi Type 106 radio receiver, a sophisticated crystal radio receiver made from 1915 through the 1920s by the American Marconi Co. for use in commercial wireless telegraphy stations. The cat's whisker crystal detector is visible on the front panel between the bottom center and righthand knobs. The Type 106 went through many design changes. Its tuning range was 3500 to 200 meters (86 to 1500 kHz). The crystal "cat's whisker" detector is visible between the lower center and right knobs. Research Engineer Harry Shoemaker was in charge of developing receivers at this time. This sophisticated inductively-coupled receiver could receive Morse code transmissions from powerful spark gap transmitters from thousands of miles away, across oceans. Controls The 4 dials along the upper part of the front panel (L to R) were: Transformer primary tap point (two leftmost dials)- this was adjusted to match the input impedance of the receiver to the antenna for maximum power transfer. The larger right dial adjusted the tap point by tens and the smaller left dial by units, giving a range from 0 to 299. Potentiometer - set the bias voltage applied to the crystal, when the battery switch (below) was on. The carborundum detector mainly used in professional receivers like this was a diode with a large band gap of about 3 volts, and a forward bias voltage of several volts from an internal battery was applied to it to increase its sensitivity. The bias moved the DC operating point of the diode to the most sensitive "knee" of its current-voltage curve. Transformer secondary tap point - this matched the impedance of the transformer secondary to the crystal and earphone to transfer maximum power to the earphone The 3 larger dials along the lower part of the panel (L to R) were: Primary condenser - tuned the primary (antenna) circuit of the receiver to the desired station Coupling - adjusted the coupling (mutual inductance) between the primary and secondary windings of the resonant transformer by moving them apart or together. This was used to increase the selectivity of the receiver. If two stations were close together in frequency and interfering with each other, the operator could "loosen" (decrease) the coupling, which had the effect of increasing the Q factor and selectivity of the receiver, to reject the unwanted station. This was a tradeoff because the lower coupling also decreased the power transfer to the earphone. Secondary condenser - tuned the secondary circuit of the receiver to the desired station. Both the primary and secondary circuits had to be tuned to the same resonant frequency to receive the station. All 3 of these controls were interactive; adjusting one changed the adjustment of the others, so tuning in a station was an elaborate process of successive approximation. When a station was adequately tuned in, the operator wrote down the settings on the dials in his logbook so the station could be found again without trial and error. Below the 3 large dials are visible the battery switch (left) which turned the bias battery off when a crystal detector other than carborundum was used, and the crystal detector (right). Information from Wenaas, Eric P. (2007) Radiola: The Golden Age of RCA, United States of America:  Sonoran Publishing, pp. 48 ISBN: 1886606218. .