Radio mirror (Jan-Oct 1923)

RADIO DIGEST ILLUSTRATED PERFECT MICROPHONE (Continued from page 1) iug formerly caused by mechanical resonance of every diaphragm microphone transmitter. It fills a need which has long beeS felt at every broadcasting station, and beeauso of its obvious advantages over every other microphone now in use, including the condenser microphone, the Westinghouse company has announced plans for installing the now device at all of its plants, which are KDKA, WJZ, WBZ, and KYW. Other stations are also considering the use of the device. Research. Work a Classic The development of the new microphone required much research and many unsuccessful attempts with other styles of transmitters. This work by Dr. Thomas is classic in the realm of scientific research and will go down in the annals of electrical history. Briefly, the carbon granule microphone, such as In use on practically every wire telephone, was discarded because of the packing of the granules and the distortion created from this. Secondly, a moving coil or "electrodynamic" transmitter was constructed. However, it was found that the resonance frequency, that is, the "tune," of the moving coil and connecting wires entered into the reproduction of the voice and music, so that this style of microphone was considered unsatisfactory also. Condenser Type a Failure Next the condenser microphone, designed primarily for the measurement of sound intensities, was tried out and met such success that it is still in practical use at hundreds of the leading Radiophone broadcasting stations. The condenser style, although undoubtedly the best yet of any microphone employing a diaphragm, still had two serious disadvantages. Its diaphragm sagged very much with use and varying atmospheric conditions, and a very high degree of amplification was required for its satisfactory operation. Eliminate Diaphragm It was then decided to attempt to reproduce the sound waves electrically by one of the several ways not necessitating the use of a diaphragm. At this stage in the development, Dr. Thomas was possessed with the idea of using the phenomenon of the great change in potential across a socalled "glowing discharge" at reduced pressures of air when a change in the length of the discharge path occurred. He believed somewhat of the same effect might be present in air at atmospheric pressure and went to work on this idea as a means of making a diaphragmless "glow-discharge" microphone. In telling of his work Dr. Thomas says: Inventor Tells of Work "A calculation showed that this effect would afford ample sensitivity at reasonable impedance, were it to be even onehundredth as great in open air. Tentative tests were made along1 this line, which seemed to show that the sensitivity in open air would not be sufficient for the purpose: also it was necessary to use a diaphragm. The writer, however, was able to show that the discharge impedance could be varied directly, without the intermediary diaphragm, by pressure variation from sound waves reaching the discharge path. Origin of Name "Glow-Discharge" "The direct current glow discharge, at low pressure, is a fairly well-known form of ionization conduction. Little has been published, however, on its characteristics in open air. Since the new microphone makes use of such a discharge as its variable impedance, a brief description of the phenomenon is thought to be desirable. "The application of moderately high direct potential between two electrodes separated a short distance in air, with enough series resistance to prevent formation of the usual type of heavy current arc, will cause the establishment of a peculiar low current, high voltage discharge, having a characteristic glowing appearance, from which is derived the name ■glow-discharge.' Nature of Discharge "The order of current is from one to 20 milliamperes or more, at voltages ranging from 200 to 1,000 volts. Such a discharge, when produced between electrodes of certain metals, of which copper is one of the best, is remarkably quiet and steady to the unaided ear and eye. The discharge path is very similar to that produced at low air pressure. "The development was completed by the working out of a low current, high voltage rectifier, with resistance-capacity filters, which permits the discharge to be struck or started by flashover, and maintains its current practically independent of discharge impedance. Units substantially of this construction have been used in the regular broadcasting programs of Station KDKA for several months." $100 FLEWELLING PRIZE CONTEST RULES 1. Contest is open to all Radiophans, whether or not they are subscribers to Radio Digest, Illustrated. The contest is open now and will close February 24 at midnight. Awards will be announced in the March 17 issue of this publication. 2. The object is to locate and award prizes on a competitive basis for the best Flewelling circuit receiving set entered. 3. Prizes are: First, $40.00; Second, $25.00; Third, $10.00; Fourth to Eighth (five prizes) inclusive, $5.00 each. 4. In event of a tie, equal prizes will be awarded each tying contestant. 5. Judges will be the Technical Staff of Radio Digest. 6. To enter the contest send working drawings and diagrams together with an article of from 1,500 to 2,500 words in length describing the making and operation of an actual Flewelling circuit receiving set. The article should tell: (a) how to make the set, (b) how to operate it, (c) helpful suggestions for getting maximum results, (d) actual airline broadcasting station receiving range using only one tube, first employing only an indoor aerial but no ground, second, using a ground but no aerial, and third, if available, using only a loop aerial. Other combinations and notations on the antenna system used will be considered in the award of prizes. 7. In sending material for consideration in the contest, exclusive publication rights are automatically given to Radio Digest, Illustrated. All articles published, but not awarded prizes, will be paid for at regular space rates. Unused manuscripts will be returned to contestants on request. 8. In deciding the winners of the contest the judges reserve the right to call for any set entered to be sent in for examination and test. Tubes. A and B batteries and phones will not be required in sets sent in for testing. 9. Manuscripts will be judged from the standpoints of neatness, clarity of expression, completeness, and actual tried success of the set described. 10. Originality in the use of various parts of apparatus other than shown by Radio Digest in the Flewelling circuit heretofore, is encouraged and even recommended. See Rule 6, however, for method to be used in determining the range. Army Net on Paying Basis WASHINGTON. — After a year's operation, the army Radio service has now reached the point where it is operating on a paying basis, giving good service on all official communications in and out of Washington. While perhaps not comparable to commercial Radio traffic systems, the signal corps Radio traffic curve. the plotting of which began in January, 1921, has risen by about $1,000 a month. In December it reached the value of $6,200 for the month. This is solely on official war and other departmental Radio traffic between stations of the army Radio net; the army handles no commercial or naval messages. During December the returns for traffic handled, when figured at commercial rates, exceeded the costs for personnel and maintenance of the whole net, including sixty stations. Radio waves vary up to thousands of meters in length. They travel in all directions and through all mediums. CONTENTS Badio Digest, Illustrated. Volume 4, Number 7, published Chicago, Illinois, February 24. 1923. Published weekly by Radio Digest Publishing Company. 123 West Madison Street. Chicago, Illinois. Subscription rates, yearly, Five Dollars; Foreign, Six Dollars; single copies, Ten Cents. Filtered as second-class matter April 27, 1922. at the vostofflce at Chicago, Illinois, under the Act of JTareta 3, 1879. END DATE NEAR IN PRIZE SET CONTEST FLEWELLING FANS FLOOD MAIL WITH ENTRIES Letters Show How Improvements Have Been Made in Circuit — Last Call for Contestants By the Contest Editor As this edition of Radio Digest goes to press, manuscripts, photographs and "drawings to be entered in the $100.00 Flewelling Set Prize Contest continue to arrive with every mail. The few remaining days before the closing date of the contest, midnight of February 24, it is believed will yield many more contributions from aspiring Flewelling fans. Marked ingenuity and clever assemblies are shown by many of the amateurs who have already submitted papers. And the results they claim! It seems that Radio Digest can be congratulated without a doubt for having made the discovery of E. T. Flewelling and his truly "flivver" super circuit. Fans Improve Circuit It is also interesting to note the changes and modifications in the circuit which are shown by some of the contestants. Greater results than with the average Flewelling receiver are claimed by some of the fans who have made distinct changes in the original circuit. Well, now a word to the eleventh-hour contestants. The date of the issue for which this is being written marks the close of the contest. Papers received after midnight, Saturday, February 24, cannot be considered in the contest. So mail in your papers today, after carefully reading the rules of the contest which are given in full on this page. Preliminary Injunction Granted in Tube Suit$ Judge A. N. Hand Gives Decisions in Patent War "All the Live News of Radio" 1 to 6 Flewelling Prize Contest Rules 2 Receiving Records Contest r .• A Yank Plant Entertains Brazil 5 Book Reviews 6 The "How" of the Simplified Super Circuit, Part IV — Theory of Operation, by E. T. Flewelling... 7 Radiophone Broadcasting Stations, Part II, Station Schedules Continued 8 Editorials; Condensed by Dielectric; In digest. Humor Column 10 A-B-C Lessons for Radio Beginners, Chapter VIII — A Crystal Detector Receiver, by Arthur G. Mohaupt 11 Honeycomb Mounting on Cabinet Top; Five Other Kinks 12 Reinartz Panel Set Design for Compactness, Part III — Construction of Cabinet, by H. J. Marx. . , 13 The Roils Royce of Radio Receiving Sets, R. D.-73; The Reader's View; About Radio Parts 14 Questions and Answers IS Radio Illustrated, a Page of Pictures IS Looking Ahead Winnipeg New "Scalp" for WCAH Station, Columbus COLUMBUS, O. — Winnipeg, capital of the province of Manitoba, Canada, is one of the new distances made by Station WCAH of the Entrekin Electric Company, Columbus, it has been announced by C. A. Entrekin, proprietor. WCAH now has the record of being heard in 27 states In the Union and two provinces of Canada. Sets Submitted in the Flewelling $100.00 Prize Contest will be shown soon. Judging from the unique designs submitted, the descriptions of these sets will be interesting reading for all fans who have been experimenting with the Radio Flivver. Watch for the series. Another Fine Article by E. T. Flewelling will appear in the March 3 issue of Radio Digest. Read his opinion on the theory of the circuit's operation, page 7, this issue. Arthur G. Mohaupt Will Tell Radio Beginners next issue how the vacuum tube works. Chapter Eight of his splendid series for beginners appears on page 1 I. Read it and keep on with the series. An Interview with Jackie Coogan should interest the young readers of Radio Digest. Watch for this feature in an early issue. More Pictures of Popular Artists at AH the Well-Known Stations are assured for readers of Radio Digest. Every issue features some of the singers, musicians, readers and other artists. You hear them nightly but like to see them, don't you? Part III of the Only Sure-Fire Radiophone Station Directory will occupy pages 8 and 9 next week. Three consecutive issues gives the whole directory. Buy the Digest and know who you hear. Newsstands Don't Always Have One Left WHEN YOU WANT Radio Digest YOU WANT IT! BE SURE OF YOUR WEEKLY COPY BY SUBSCRIBING NOW SEND IN THE BLANK TODAY NEW YORK. — Judge Augustus N. Hand, in the United States District Court for the Southern District of New York, has handed down decisions, granting preliminary injunctions in three suits brought by the Radio Corporation of America for alleged infringement of the De Forest audion patents by the manufacture and sale of vacuum tubes for Radio purposes. The first of the suits was that against the La France Import and Sales Company, Inc., and others who are manufacturing and selling a vacuum tube known as the La France" detector and amplifier. The second suit was against Harry Rosenthal and others who are manufacturing and selling a vacuum tube detector and amplifier known as the "Perfection" tube. The third suit was against the Radio Guild, Inc., a dealer in the "Perfection" tubes. One of the principal defenses urged upon the court for a denial of the preliminary injunction motions was that the Radio Corporation of America had no right to maintain the suit because the De Forest Radio Telephone and Telegraph Company was the owner of the De Forest audion patents. This defense was overruled by Judge Hand for the present, in granting the preliminary injunctions. ASKS FEDERAL QUIZ (Continued from page 1) pose, tendency or effect of which is to give exclusive rights or special privileges in the reception and transmission in interstate or foreign commerce of messages by Radio, and " '(D) Such other facts as, in the opinion of the commission, may aid the House of Representatives in determining whether in the foregoing respects or otherwise the antitrust statutes of the United States have been or now are being violated by any person, company or corporation subject to the jurisdiction of the United States.' " Publisher. 4.7 123 West Madison St., Chicago, Illinois. Please find enclosed check M. 0. for Flvo Dollars (Six, Foreign) for One Year's Subscription to Radio Digest, Illustrated. Name Address , , , , , City State „.... New Tropical Station Opens Direct Route to Honduras WASHINGTON. — The opening of the new Tegucigalpa station of the Tropical Radio Telegraph on December 1 provided the first direct communication from the United States to Honduras. Previous to date the only available route was via AllAmerica Cables to La Liber tad in El Salvador and thence over the land lines of that government and those of Honduras. The new station is equipped with the latest type of tube transmitters, with a power of 20 kilowatts and a normal operating range of 1,500 to 2,000 miles. The Navy Department has begun the publication of the Communication Bulletin, issued in the Interests of increasing the efficiency of Naval Communication*, especially through greater rapidity and accuracy in handling messages by Radio.