WIRELESS NEWS.

Press, Volume LX, Issue 18141, 2 August 1924, Page 9

WIRELESS NEWS.

RESONANCE IN RADIO. USES FOR THE POTENTIOMETER (specially WHiTTzjf *oa "thb press.") (By "Electra.") When tre tune a radio set we are adjusting the cirenits so that they -will be in resonance with each other, and the transmitting station. A clear understanding of this phenomenon is necessary for the intelligent operation and construction of a radio set. Resonance is dependent upon inductance and capacity. These two elements are necessary to establish in a circuit wave-length or response to frequency. All circuits have resistance, which is present in the conductors, condensers, and inductnnees. There are. therefore three quantities—inductance, resistance, and capacity—in a circuit. _ The amount of current that will flow in a circuit depends upon the strength of the voltage and the resistance of thp circuit. These two forces would establish a condition that could be easily handled it' the third quantity, frequency was negligible. Voltage is that energy which forces current through a circuit. Frequency is the number of times per second that force is applied. Current flow, therefore, :s .-.pntroHed not only by the force but also upon the number of times per second that force is applied. If a constant voltage is applied, a circuit and the frequency are steadily increased from a low to a high frequency, it is found that the current value increases to a certain point and then decreases. The frequency at which maximum current passes will be found to be the hi turn! frequency or wave-length-of the circuit. At this point the frequencv of the energy applied is the same as the nntural frequency or wave-length of the circuit. This condition is known ls resonance. If the resistance in the circuit is high, it affords a constant opposition to the current flow. This condition results in broad tuning. If this resistance is high, the tuning becomes broad, and long-distance, reception impossible. Remove this resistance and the tuning becomes sharp, and interference is reduced if not eliminated.

POTENTIOMETER USES. A potentiometer is a very useful device in any radio receiving set. The place where it is most .'often employed is in radio frequency amplifiers, where it- is used to, prevent oscillations by controlling the grid, voltage of the r:idio frequency • amplified valves. When used for this purpose the two outside terminals of the potentiometer are connected to the two "A'» battery terminals, and the slider is connected to the grid return of the radio frequency amplifier tubes. Plato Voltage Regulator. Another use for a potentiometer is to vary the plate voltage for soft detector tubes. This may. be accomplished by connecting the negative "B" battery wire to the slider on the poton tiometer, and then connecting the resistance coil of the potentiometer across the "A" batterv. With the potentiometer connected in this manlier it is possible to vary the "B" battery potential 6 volts —i.e., when a six volt. "A" battery is used to light the filaments. To Boduce Be-radlatlon. A third use for a potentiometer ' in a receiving' set is to increase the resistance of the aerial, and in that way reduce tho radiation from regenerative receivers. When the potentiometer is used for this purpose" it is connected as a rheostat rather than a potentiometer, for the slider, of the in*

strument is eennected to tho aerial, an one side of the resistance is connected to the aerial terminal on the receiving set. . ' The resistance of the average potentiometer is between 100 and 500 ohms, and for receiving sets a potentiometer of about 400 ohms resistance is usuany required. NOISY RECEIVING SETS. Scratching noises in a radio ing set may be due to one or more 0.. , several causes. . . Those p rsons having sets that aro scmtchy will do well to read ° ve, \ , e following list and then look over their sets for the points mentioned. Where to Look. The first place to look for is the aerial a-d tne ground. If there is any corrosion in any of the 2 they should be taken apart ancl c'eaied, then re-soldered. Any joint that w_ not soldered is liable to cause noises in the phones. , The next place to look for troub e is on the tube prongs If there is any corrosion here it should be filed off, and the prong preferably given a coating of solder Use resin as flux in this terminals on the sockets, rheostats, nnd other parts of the set, if loose, will cause scratchy noises. All nuts should be tightened with a pair of pliers to eliminate any chance overlooking one nut. _ _ , Loose-soldered connexions m any or the leads in ~ho set will cause noises, and also clicks, that are easily traced by touching the wires when the phones are in circuit and the tubes lit. Any friction bearinfis on variable condensers, variometers or variocoiiplers will cause any amount of r"'SPS if n"t properly designed. Itwoud be ** ■ to rmt fietnil connexions on all t*e equipment that now have this vr>e o benrirf and fore<?o the or rJeaniwx the shafts and rods everv time the set becomes noi«y. nooses are due flo loose nhone connexions. is easi v t,rn<-«d' bv shaking: tlie phone rord while the ohones are to <se+, with the tubes turned on. 'be small nuts on the t.ernvnnls on the oliores -fV>V'Ps often liave a habit of becoming loose.

Battery Connexions. Many of the noises in a radio set can be traced to tlio _ cause these noises resemble static it is seldom that any other source for them is thought of. Poor battery connexions cause more "static" than any other one fault. "A" battery connexions should be made by means of a dip which can be made to grip the terminals of the battery. It is preferable that the "B" battery connexions also be made by means of a smaller clip than used on the storage batterv; these clips should have a very strong gripping power. If you are positi™ 11,0 connexions of the batteries are OK and the "static" still continues, test the "B" batterv for "dud" cells. One bad cell in d. "TV' battery will cause more trouble than enough. Other sources of noise trouble are—burnt out Kadio frequency or audio frequency transformers, phones, or a broken wire in inductance coils. GROUND CONNEXION. The installation of a radio set seems to mean to most new radio fans simply the putting up of a good aerial. The ground connexion for some unknown reason is ignored as far as an efficient connexion goes. In putting a set in a house it should always be remembered that a good ground connexion is just as important as a good aerial. In the last few weeks quite a number have spoken to me about the indifferent results they are . getting and in all cases except one, the trouble to my mind lay in the earth connexion. A poor earth will cause broad tuning, so those that think their sets are not selective should look to the earth before pulling the outfit down.

HERE AND THERE. At the annual commencement exercises of Hamilton College, at Clinton, N.Y., last month, the honorary degree of D.Sc. was conferred on Hiram Percy Maxim, of Hartford, Conn., president of the American Radio Relay League. Radio exports from the United States during April amounted to 299,903 dollars, an increase over April of • last year and over tho total for March, although loss than the exports during January and February of this year. During the first four month of this year, the U.S.A. has shipped abroad 1,222,685 do r nrs worth of radio materials, whereas year's total for this period was 775,324 dollars. Eight new broadcasting stations have been recently opened along the Canadian border; in Alberta, Ontario, Quebec, and British Columbia. (And they say broadcasting is on the wane I) Questions on radio matters 'will be answered in this column. Address all correspondence to "Electra," care the Editor, "The Press."