Regarding the choice of wire to be used, it becomes evident that even bare copper or other wire may be utilized when desired, as Mr Rogers has pointed out in the above contribution. The size of this wire should be about #12 or 14 B&S gage, the heavier the better.
The official US Navy report of tests on the Rogers Underground System mention that no increased efficiency is obtained by using more than one wire, and that this may be a # 12 or 14 B&S gage, weather-proof or rubber-covered copper conductor. In any case, the free end of the wire should well taped, and preferably covered with some rubber cement, so as to keep it insulated. Experiments have been tried both by Mr Rogers at his Hyattsville MD laboratory, and also by the Navy Department, with underground aerials in terra cotta pipes, but this construction is rather expensive, and the results obtained do not justify its use.
Other forms of wire used both by Mr Rogers and the Navy Department experts include lead-covered telephone cable, which is, of course, thoroughly damp-proof, while a conductor holding considerable favor with the inventor is the heavy rubber-covered, high-tension, auto-ignition cable. This is highly efficient for aerial requirements, as it is stranded and therefore of low high frequency resistance.
In any case, a little common sense and logic will give the answer to many of the simple problems arising in connection with the installation of these aerials, such as, for instance, the length of aerial to be used for a certain range of wavelengths. It is manifest that the longer the wavelength to which it will properly respond. Considering that an antenna is used having a length of, say, 150 to 200 feet, then practically all the shorter wavelengths up to 600 meters and more should be readily picked up on this antenna, especially with the variable condenser hooked up in series with the primary of the loose coupler, as shown in the accompanying diagrams. Naturally the wire buried in the ground has a higher electrostatic capacity than the old style antenna wires, elevated 40 to 50 feet above the ground, and we can reduce this capacity as desired, so as to tune any certain wavelengths, by connecting another capacity in series with it: in exactly the same manner as short wave lengths are tuned in on the regular elevated aerials, by connecting a variable capacity in series with the antenna circuit, and the primary of the loose coupler. Long wavelengths are tunable by using large condensers and loose couplers preferably.
Spiral or Loop Aerials
As shown in the diagram, Fig. 7, interesting results were obtained with a spiral antenna, composed of a dozen or so turns of insulated wire, such as a high tension cable or # 14 RC solid conductor lowered into a well. Both with and without water in it.
As pointed out in the original article on the Rogers underground system in the March issue, very promising results have been obtained in transmitting with the underground antenna, and Fig. 8 shows how a small transmitting set was operated with such an aerial, coupling the exciting or spark gap circuit with the antenna oscillatory circuit by means of a two-coil oscillatory transformer, L, C. In this case two metal plates, about one yard square, are placed in the earth adjacent to the well, one of which connects with the secondary, S, of the oscillation transformer, while the other plate connects with the free end of the spiral antenna.
If the spiral antenna is used, it should be placed on its vertical axis, and it should be placed in the vertical placed in the vertical plane as shown as shown in Figs. 7 and 8. Excellent results have been had should be obtained in transmitting with the underground antenna, with the usual insulation incident to the form of conductors above specified, where the transmitting set is one employing an audion oscillation generator. The voltage in this case will not be extremely high and special precautions need not be taken to provide extra heavy insulation on the buried antenna. The wire in such a case, however, should be especially. Official tests by the US Navy have shown transmission by radio over 50 miles with the Rogers underground antenna. The wire in such a case, however, should be especially well insulated to stand the higher voltage.
Regarding loop aerials in general, it would appear that we can expect a great deal from them, as some of the really remarkable results achieved during the war would seem to point out. The number of turns and the amount of wire to be used in a spiral wire to be used in a spiral antenna, such as shown at Figs. 7 and 8, will vary of course for different wavelengths, etc., and here is where the radio Amateur will have a chance to carry out some original experiments, which may net him some real knowledge, fame and money. Another form of loop antenna, so-called, and which has been tried out several years ago with such success that European stations could be copied in a laboratory located in Florida, is one composing a square form, several feet in height. This was used, as just mentioned, to receive stations using fairly long wavelengths, say from 8,000 to12,000 meters. Here the insulating form was wound with a layer comprising several hundred turns of insulated wire. This antenna was successfully used in some tests made by Marconi radio engineers at a laboratory in Florida several years ago. Trans-Atlantic radio reception was effected at the radio laboratory of Union College, Schenectady NY, just prior to America’s entrance into the world war. This aerial comprised about two dozen turns of # 14 or 12 bare or RC wire, mounted on porcelain know insulators screwed on the inside wall of the laboratory. The turns were spaced about 3 inches apart. The inside turn was 3 feet square. Flexible leads, fitted with clips, serve to connect as many turns as desired.
- Rays & Radiation Phenomena
- CROSSE’S ACARI