The Elimination of Static

Radio Record, Volume II, Issue 21, 7 December 1928, Page 3

The Elimination of Static

T. he Story of Man's Accomplishments in His Struggle against Nature —

ai all the problems that ai) have ‘confronted radio engineers since wireless was, the elimination of static, has been the most mes «baffling. To-day its successful remains an unsolved problem thourh static-reducing devices by the score have come on the market. Certainly static has been reduced, but a’ the expense of the signal-strength. Those which have attained moderate success have been very complicated and add -‘rreatly to the gost and complication of the receiver. The fundamental problem lies in the very nature of statie. A few months back there appeared in the "Radio Record" an article explaining the phenomenon as it is known at the present time. Static, to briefly reiterate, is a charge of electricity at liberty in the air. It is entirely different to the electricity known to us by use. Static is a charge, while electricity in use is a flow. Alternating current of the latter type is used to convey the signals from their point of origin to our receiving sets. Alternating current signifies a rapidly flucftuating voltage which tises and falls at a definite rate. This definite rate (frequency) pz ‘teular to each station permits of selectivity. ptatic electricity on the other hand isnot a flow, and for this redson cannot have a frequency. Were it te be of 4 definite frequency it could be tuned out of any set just as an unwanted station can. be. ‘Statie Elimination. FrRoM its very nature then, the elimination | of stat’ o 4° a problem of

some dimensions. As it enters the set with the signals, it is difficult if not impossible to separate it from the signals, for anything that tends to reduce static will reduce the strength of the signals. The most logical method of reducing this annoyance it to increase the power used in broadcasting. If the signal strength can be made consider-

ably greater, then the amplification may be reduced while still giving satis-' factory signals. This explains why those situated near a powerful station do not suffer with the annoyance like a listener situated more remotely from the transmitting station. There is, however, an obvious limit to this method of control. Underground Antennae. QF the various devices to combat static the most successful is perhaps the underground antennae. In this direction great research has been carried out by Dr. J. H. Rodgers, Hyattsville, United States, and to him one has to refer for the most authentic inf .rmation on the subject. ’. (he principal claim covering this type ef antenna defines the system "comprising an antenna extending horizontally, substantially parallel to the surface of the earth, and insulated therefrom, a metallic covering the anterina but insulated therefrom, and in intimate contact with the earth throughout its length, signal instruments associated with the antenna and \ a balancing connection at the other end." Sueh is the definition given by the inventor. Actually the antenna consists of a length of insulated wire enclosed in a metal sheath, such as a lead cable puried sufficiently to that the sheath makes good contact with the ground, and parallel to fis surface, the lead-in being brought fo one side of the coupling inductance, or, as is usual, the aerial eoil. The other end of the coil is grounded in the usual manner. Of this there are many variations. One can place the shielded cable on top of the greund, but in contact therewith, the cable on supports so that it is supported a few inches above the earth, and several arrangements, including the grounding of the farther end. of the cable. In another type the ground connection is replaced by a length of.cable, as is used for the antenna. There are many other variations. of the underground antenna, but most of them have proved less satisfactory than | the original. Rogers antenna,

Experiments. [}*PERIMENTS with a real Rogers antenna, using a sensitive heterodyne, showed that a range of 500 miles at night in the winter might be expected with loudspeaker volume, from a station having a power of 1000 watts. The static level was very much lower

than when using an aerial 40 feet above the ground and 80 feet long. Although the volume on distant stations was much less than with the aerial a well-defined reduction of static was noted. However, when using the wunderground antenna with a _ seven-valve tuned radio frequency set of a well known make the results were much poorer than those obtained with the superheterodyne, due to the lower sensitivity of the r.f. set. Stations 500 miles away which came in well with

the aerial could not be heard with the underground antenna, and this was made with the underground antenna arranged in such a manner as to receive the signals of the station to the best advantage. On the local stations, however, the performance of the set was very satisfactory, and while the static level on the aerial was so far down as to be barely noticeable, a difference could be noticed when the underground antenna was employed. Hxperimenting with other than the Rogers system proved them (the Rogers) vastly superior to any other. Other Underground Antennae. A CORRESPONDENT to "Radio News" suggested another wunderground antenna, or rather two. ‘The first was to consist of four four-inch cylinders; around each was toe be wound 60 feet of insulated rubber-cov-ered wire, these to be soldered to the lead-in wire. This lead-in wire was to be protected from atmospherics by a lead tube running from one foot under the ground to the aerial terminal of the set. The apparatus was to be buried five feet under the ground in porous soil. Secondly, a rubber-covered wire was to be lowered into a well 75 feet deep, the lower end to be sealed to make it impervious to water. The receiver was to be shielded to prevent the picking up of static.

_- a ee ee A (SORRESPONDENTS have asked for means of reducing static, and, after an exhaustive search, the following article is presented as a brief resume of the accomplishments of man in his struggle against unsympathetic Nature. While some of the methods may sound a little technical to some listeners, yet an endeavour has been made to use as few technicalities as possible and to give, where possible, the suggestions of those who have pioneered the field. There are great possibilities and opportunities for those interested fo do some interesting research work. 3 EE ERS ae Ss Se Se Se og es et se SS SSeS SS a ee as ee ee en ee ee SS FSS Ss SS 3 SS Ss SS SSS SSS = st -F — 3 SS SS SS SOV TLE ESE SS SS SS

i Dr. Rodgers gave his opinion on the proposition. Commenting on the four eoils he said that in his opinion one of larger size would be better, adding, "By the use of underground and underwater antennae, static is reduced, and this is the most effective means yet found. I believe it is only a question of time before someone will devise some form of earth antenna that will further reduce or eliminate atmospheric disturbances. Best results with any form of. these collectors are only attained when buried deep, at least to the depth of ‘water earth.’ "Ag it is a well-known fact that intensity of signals remains almost constant even when antennas are lowered far below the surface of the earth, and, conversely, ‘atmospheric static’ reduces rapidly; if a form of antenna could be devised which would take advantage of this, static would be greatly reduced. Shielding the receiver and certain parts of the leads might help to solve the problem," Dr. Rodgers has been quoted fully because his ideas are somewhat contrary to the accepted theory that radio signals decrease rapidly as they descend the earth. The problem is interesting and deserves some thoughtful consideration and experiment. | The ground antenna, although receiying less power than that collected by an aerial, has a number of compensating advantages. They are strongly di-

rectional, receiving most power when they lie in the direction of the station or stations to ‘be received. Also, they do not develop the usual trouble during local thunderstorms. Dimensions of a Rodgers Antenna. [HH length of wire to be used as an underground antenna depends on the wave-length of the station to be received. Thus, for the longer wavelengths, longer wires should be used than for the shorter wave-lengths. The wire should be heavily insulated, and where possible encased in a lead con: duit. Inearth of the average range of moisture, 75 feet long may be expecte:l to give satisfactory reception from 150) metres to 500 metres, Wire such as used for the ordinary aerial, stranded or solid, is suitable. Of necessity it should be used only where a good aimplification system is in use. Other Methods. A HIGH resistance of 100,000 ohms or more, connected between the antenna and the ground terminals of the receiver will bypass a greater proportion of statie than signal because the signal frequency is the frequency at which the receiver circuit is resonant. This scheme gives the effect of reducing the static, although reducing the signals at the same time. Considerable improvement may sometimes be effected by loosening the coup-

ling between the aerial coil and the rest of the circuit and tuning the aerial circuit. The loosening of the coupling reduces the amount of energy both sig nal and statie entering the secondary circuit; but the tuning of the aerial circuit improves the strength of the signal in that circuit. A erystal detector may be included in the serial circuit in parallel with the aerial coil. In this case the peak crashes are considerably reduced, but signal strength will also be reduced. The use of the loop und indoor aeriai will improve the ratio of signal strength to static, but as the set itself has to be more sensitive static is ofteu brought up to where it would have been otherwise. Still, if one has a good set the indoor aerial will effect a very con siderable improvement, A long low outdoor aerial, especially if the set has a coarse aerial tuning arrangement, is preferable to the usual type.