In the early days Marconi, and those who followed him, thought that a high vertical wire, that is, one sticking straight up in the air, was all that was needed to get distance. On ships the masts are never very high and so the late Lieutenant Hudgens of the U. S. Navy tried stringing the wires of the aerial down to the bow and stern of the battleship Kearsarge to give the wires a greater length. This sloping aerial gave so much better results than the straight, or vertical aerial that he then suspended the wires between the top of the masts of the ship and, lo-and-behold, it worked even better than before and thus it was that the T, or flat-top aerial came to be.
To get the best results the aerials of two stations communicating with each other should both be vertical or flat-top, that is, a vertical wire will not receive from a flat-top nearly as well as from another one that is vertical and this is just as true the other way about. As all ships are fitted with flat-top aerials and as the Eiffel Tower aerial is neither the one kind nor the other but a sloping aerial and hence would receive from a flat-top as well as from a vertical aerial the Navy Department decided to use the T or flat-top aerial on the Arlington station.
We assembled, tested and put up the three flat-top aerials between the towers and connected them together so that in effect a single long aerial was formed. Porcelain insulators of the kind on which high tension power transmission lines are carried are used to insulate the aerials from the towers. The leading-in cable runs from the aerials to which it is connected down to the operating room through a copper tube set in a glass window.
The ground is formed of copper wires buried deeply in the earth and radiating in every direction from the station. This network of wires extends over, I should say, ten acres, and this, of course, makes a very good ground.
The current for energizing the sending apparatus is taken from the lines of the Potomac Light and Power Company; this runs an electric motor of 200 horse power which in turn drives a 100 kilowatt alternating current generator; the current from the latter flows through a transformer which raises the pressure of it to 25,000 volts. Next a battery of compressed air condensers are charged with this high voltage current and this is discharged by a rotating spark-gap. This spark-gap has a wheel, on the rim of which is set a number of metal points, or electrodes as they are called, and around them are an equal number of fixed metal points or electrodes.
When the wheel revolves sparks are made only when the electrodes on the wheel and those that are fixed around it are exactly in a line. Now instead of a few big sparks taking place every second, a thousand smaller ones occur in a second and this makes a whistling sound which is heard by the operator who is listening in at the distant station. The high frequency currents set up by the spark-gap then surge through an oscillation transformer which increases its pressure and finally into and through the aerial wire system where they are damped out in long electric waves.
The Morse telegraph key is placed in the receiving room and it works a control switch in the sending room. The control switch breaks up the current that flows from the generator into the transformer into dots and dashes.
The receiving instruments have both electrolytic and crystal detectors, the other parts being made up of the usual variable condensers, tuning coils and oscillation transformer and head-phones.
Well, at last everything was all ready for the final company test and I was mighty glad of it for things were getting very much on my nerves. A cableless station is altogether too big and cold-blooded a proposition for a fellow who likes a little excitement once in a while.
The Navy Department had fitted out the cruiser Salem with a sending and a receiving apparatus exactly like that of the Arlington station except it was very much smaller.