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Show (KdlteiJ by O. Douglas Wardrop. Editor of Kadio Merchandising.) l ; Types of Loops Which Can Be Constructed at Small Cost. By HARRY GEORGE I Admitting that static is a bugbear to radio, it knows no favorite type of set ; it affects all, but engineers have designed de-signed circuits and methods of reception recep-tion which at the present stage of development de-velopment can be termed as highly satisfactory sat-isfactory means. One of the greatest steps along these lines Is the development of the loop aerial. It Is a well known fact that good summer reception can be obtained ob-tained with the aid of a loop aerial and one or more stages of radio frequency. Even distant signals have been copied In the hottest summer months on certain cer-tain seml-fnvornble nights. Itut to get down to the point of our talk. It has been said that a loop will pick up but 1-10 the signal voltage that could be obtained with , the use of an outdoor aerial. If this is so It is easily seen that we must Increase or amplify this signal to such a value that It will operate a detector; the method of wiring up and operating a radio frequency amplifier has been published In detail many times, therefore it will not be given now. Our thought is the construction of the loop Itself. In laboratories and work accomplished by the vast number of radio experimenters experiment-ers different types and sizes of loops have been used, ranging in size front email colls one inch in diameter, honeycomb honey-comb colls and receiving coils of various vari-ous tuners up to massive single-turn loops measuring 10 feet on a side. Best Type of Loop. Experiments proved that the best type of loop for use on the broadcasting broadcast-ing wave lengths measured about S feet on a side and consisted of but a single turn of No. 18 green and yellow single conductor lamp cord. This loop was tuned by means of a .0006 variable low loss condenser and the results accomplished ac-complished by it fully equaled those obtained with an outdoor aerial measuring meas-uring 75 feet long. Owing to its awkward dimensions it was impractical for home use. There are. however, smaller and more convenient con-venient sizes to handle which will give very good results. The Illustrations will give the experimenter expe-rimenter an Idea of types of loops which can be constructed at a very small cost. Figure 1 shows the loop used in the Sleeper Monotrol receiver. The crosspleces measure 27 Inches, or 13 Inches on a side. It is wound with 10 turns of standard flexible loop wire spared one-half inch apart, the outside turn measuring 18 Inches. It is provided pro-vided with a set of taps, which are connected con-nected to the 2d, 4th, 6th. 8th and Oth turns. This arrangement, which Is found in no other loop, performs the unique duty of controlling the potential on the grid of the first tube, thereby eliminating the usual potentiometer. The switch does not vary the Inductance Induc-tance of the loop. The frequency is only varied by the condenser, which is shunted across its terminals, the lower low-er one of which is connected to the filament and the upper one to the grid of the first tube. Other Kinds of Loops. Another type of loop, of the pancake type, which will afford Interesting food for thought is shown in Figure 3. This loop was experimented with by H. G. Silbersdorff of Jersey City, N. J., and has the added feature of being able to not only rotate on its axis but can be tipped to any desired angle as well. Experiments with the use of a resonance reson-ance wave coil led up to the loop in its present form, and it was found to have certain defined advantages over the average loop. It seems to at least partly solve the great summer question of signal to static ratio. When tipped at certain angles the static is weaker and the signal stronger. The theory is as follows: If radio waves travel parallel to the surface of the earth and static disturbances travel in a more or less perpendicular path to it the adjustment of the pick-up coll can be so arranged to pick up most radl.i waves, which Is at such an angle that It will pick up a minimum of static waves. The crossarius of the loip measure IS inches each and the outer framework frame-work pieces measure 13 inches each. Thirteen turns are made, which are , spaced three-eighths of an inch apart. C-shaped brass angle pieces are fastened into the corners of the outer frame, which serve to support the inner crossnrnis. The entire loop is tuned by means of a .001 variable condenser. Srill another form of loop is shown in Figure 3. This is known as the box type and, while it requires more room to set up, is claimed by many en-, gineers to be more efficient than the ordinary spiral or flat pancake loop. A good size to' use for the broadcast waves measures four feet on the arms, the ends of which are provided with bakelite or other Insulating material in the slots on which are wound 10 turns of loop wire, five on either side of the lower upright support. Like the (eher types, it is tuned wifh a varialflt condenser and is recommended highly for use with supersensitive receiving instruments, owing to its large dimensions. dimen-sions. New York Evening World. |