The Rogers Underground Aerial for Amateurs
Since the publication of the original article on the Rogers Underground Wireless System, published in March, 1919, the Editors have been besieged by hundreds and thousands of letters from radio experimenters in all parts of the world, asking for data on the construction of the Rogers Underground Aerial suited for the requirements of the Wireless Amateur. The original article contained a great deal of valuable data, which should be carefully read and digested by every radio man, whether he be a student or a professional. In the present article an effort has been made to answer some of the questions which have seemed to annoy the average radio “bug” considerably, — especially those residing in cities where it is difficult and frequently impossible to bury an aerial longer than a few feet. We may say right here, that for those experimenters so situated, there is a solution, or in fact, two solutions, namely — to use a spiral antenna, such as has been tried out successfully in US Navy tests on the Rogers system, and which spirals may be buried in the ground a few feet, or placed in a well or a body of water; and secondly, for the experimenter who is not allowed to disfigure an apartment house or other dwelling with a ugly-looking aerial, there is a newly developed loop antenna, which can be used right in the radio room. Indoor aerials have been greatly perfected during the war, and now by means of greatly improved and highly sensitive wireless receiving instruments and amplifiers available, particularly those using audions as detectors and amplifiers, they are excellent, and satisfactory results are obtainable by means of a concentrated loop or spiral antenna, small enough to be placed in the radio laboratory.
For the present, we will listen to the sound advice given by our mutual friend, Mr James Harris Rogers, on some of the practical outstanding features of his underground system, used in conjunction with straight-away single wire underground aerials, as well as loop aerials. Among other things, Mr Rogers has the following to say regarding the installation of simple underground aerials:
Mr Rogers Talks to the Amateurs
“The first installation of my underground antenna was made in the woods about a mile from my laboratory and consisted in burying wires in the earth; the wires radiated from the station as the spokes of a wheel, — some wire bare and some insulated; their lengths varied from 200 to 1,000 feet. ( Figure 1)
“It is obvious that a number of persons can receive at the same time, one operator to each wire. There is no interference. Figure 1 shows 8 wires and a bipolar selector swirch connected to the primary receiving circuit. With this switch any individual wire may be grounded, or any two wires may be used. Bare wires give the loudest signals but static is more pronounced. The deeper the wires are buried, the better the signals, with a corresponding reduction of static. Short wires show a remarkable degree of directivity; long ones to a lesser degree and in proportion to their length. (See Figs. 2 & 3)
“When using two wires at right angles to each other, signals are heard from any direction. (Fig. 4)
“The system works best in fresh water or very wet earth. The primary circuit should have a variable condenser ) 0.001 mfd or higher capacity) in series. When insulated wires are covered with metal, lead, iron, etc., some remarkable results are obtained. These wires may be entirely enclosed in an iron pipe, for instance (Fig. 5), or the joints may be connected by rubber hose”. (Fig. 6)
“Regarding the tests with loops I will state briefly that I have successfully tried different forms and sizes.
“I first had a well bailed out and lowered a loop antenna into it; the well was 50 feet deep (See Fig. 7). The signals were as loud at the bottom as when above the earth. I next had the well filled with water and the results were the same, excepting that the note of the sending station became higher and higher as it was lowered. Upon revolving it around, I found the directional characteristics were the same in the water as when out. These tests were made about 2 years ago, and I at once realized that the loops or cages could be used in the dugouts of France, or on submarines when submerged.
“Regarding the dimensions of loop antennae used on submarines, these coils measure about 3 feet square in some instances. The wires are very heavily insulated and placed in a box filled with pitch, the connection are led below and the coil can be revolved for directional observations.”
Kind of Wire Used for Underground Aerials
Most of the inquiries from Radio Experimenters and those intending to install experimental stations, and wishing to make use of the “static-proof” Rogers underground antenna, on which signals may be received even through a thunderstorm, indicate that the greatest problem to solve seems to be the size and the kind of wire to be used, and how it shall be buried. Some very excellent results have been obtained in experimental work carried out at one of the leading American universities with aerial conductors laid on the ground, and where the experimenter has the time and space to try this out, he may gain some useful and valuable knowledge by experimenting in this direction. Ordinarily the wire, of whatever kind it may be, as used when installing the Rogers underground aerial, is buried about 3 feet deep in the earth. For most amateur requirements, the wire need only be about 100 to 200 feet long, and so the digging of the trench is not such a great problem; in fact, it can be plowed open, at least part of the depth, and where rivers, brooks or ponds are available the insulated wire can be placed in them directly and allowed to rest on the bed.