The early receivers fed anything that impinged on the antenna directly into the operator's headset. Thus the operator working a vessel on one wavelength would be interfered with by a second vessel transmitting on a different wavelength. An operator had no way of tuning in the wavelength he wanted and attenuating the rest.
This tuner used a crystal (diode) detector, instead of the older magnetic detectors. The crystal was more sensitive (weaker signals) and required no winding of a spring motor.
This detector was a piece of galena rock mounted in a carrier. A small wire (cat's whisker) was poked about on the surface to find a sensitive spot (signals heard) and then secured in that position.
A crystal detector on its own will not work well with a very weak signal, but if a direct current voltage is applied across it, the same weak signal will be heard. (Diode's E vs I slope isn't linear.) The operator would adjust the potentiometer control to vary this current and find the 'sweet' spot.
The "billi condenser" is an insulated wire wound tube in which a sliding metal surfaced tube is inserted. There is a small capacity between the coil on the outside and the metal on the inside. The amount of capacity is directly proportional to how much of the metal tube is inserted. The term 'billi' is an abbreviation for 'billion'. And in this case stands for 'billionth of a Farad' or in modern terms 'nanoFarads'. (milli, micro, nano, pico)
Probably appeared on the market around 1908.
Spark Station Equipment
