Radio Broadcast (May 1928-Apr 1929)

~Z_ RADIO BROADCAST 3T Fig. 3 shows the set up of the coil tester. It comprises two oscillators and a radio receiving set. One of these oscillators is fixed, say at 300 meters, the wavelength to which the receiving set is tuned. The other's wavelength depends upon the inductance of the coil Lx under test and is brought to 600 meters by the vernier C3. C4 is a compensating condenser which can be adjusted to bring the reading of C3 to exactly 50° when using a standard coil. It will be noticed that the second harmonic is used here for greater sensitivity and also that the coupling between the oscillators is extremely loose, as we have the r.f. gain through the receiving set to make up for it. Thus we are able to get a very sharp reading on this tester. It will also be noticed that the two oscillators differ in wiring in this tester. The fixed oscillator uses a modified Hartley circuit, i.e., Fig. 3 Coil in Shield Phone i 0 ___ 0 i Coil in Shield OscSocket Jacks"7!— ^ ' AF. LyJ AF. A.F.Transformers •' Insulated Strip carrying contacts for Stators of gang Condenser Toggle Switches to switch to different units of gang Fig. 2 — Suggested layout for oscillator of type shown in Fig. 1 utilizing a coupling coil for feedback, whereas the other oscillator gets its feed-back through a resistance which is common to both plate and grid circuits. This eliminates the need of a tickler coil, and the coil under test has only two connections made to its extremities. Also a filter is provided in Lf, Cf which reduces the coupling between the two oscillators. The two oscillators are shielded from each other by partitions and the only coupling is through the common batteries, as in the case of the condenser test, except that it is reduced still further in the case of the coil tester by the use of the filter. In using this tester set C4 so that an average of a large number of coils will come at 50° on C3. Limits may be obtained for C3 by measuring the extremes of a large number of coils. For instance, if the average coil is 200 microhenries and a coil giving a reading of 60° is 195 microhenries, and a coil reading 40° is 205 microhenries, then ten degrees on the tester corresponds to five microhenries in 200 or 2| per cent. If 1 per cent, tolerance is allowed this means 4 degrees. It has been found possible to hold coils to tenths of one per cent, with this tester, as it will easily show a difference of a few hundredths of one per cent, between two coils. In actual use the operation of this tester „50mmfd. ■ UX201-A 0.006 mfd. Oscillator 6V. ^ -Circuit of beat-frequency oscillator for testing coils is very rapid if the coils are at all close, as an audible beat will usually be heard the minute the coil is placed in the jig, denoting that the coil is easily within required limits, so that in most cases it is unnecessary to adjust C3. A word of caution is proper here regarding the use of B-power units to operate these testers. While the testers themselves will operate satisfactorily on such devices they will usually cause considerable external annoyance to near-by receivers due to radiation through the power lines. If sets are being tested in the same building they are apt to pick up the beats when they are tuned to the same wavelength as the tester. The foregoing discussion will no doubt show that the use of beat frequencies in inspection apparatus is much to be preferred to previous methods of aur;d and visual measurement, not only for accuracy but for speed as well, and consequently is well worth adoption in all plants when precision is desired at low cost. BOOK REVIEWS Advertising By Radio, By Orrin E. Dunlap, Jr. The Ronald Press Company, 1929. Price $4.00. In this new volume on radio advertising appear figures for the returns of many recent commercial broadcast features. The author has had access to the sales-promotion material and tabulations of mail return of the National Broadcasting Company and its affiliated stations and also those of won. These are quoted liberally throughout his book and should make the volume of immediate interest to all solicitors selling time for broadcasting stations, because any shred of material giving tangible proof or suggestion of proof of the medium's effectiveness is welcome to them. To one familiar with all the problems of commercial radio broadcasting the rather broad scope covered by the title of the book and the headings of the chapters is hardly fulfilled. But Dunlap provides the complete answer to the question, "Does commercial broadcasting bring mail response?" His observations on broadcast programs are those of any expert listener and critic. He levels a few richly deserved shots here and there at announcers for faux pas familiar to radio listeners. In common with the entire broadcast industry he sidesteps the most important point in appraising the value of the good-will program, namely, " Does broadcasting actually influence sales and at what cost?" Conclusive proof that thousands of people send for a cross-word book or a bridge score pad is only indirect and inconclusive evidence as to actual sales return. Considering that commercial broadcasting is now entering its eighth year, the advertiser certainly has the right to expect some tangible proof that that warm feeling around the heart which the radio listener is supposed to have for those who sponsor programs has in one instance or another actually increased sales volume by a definite number of dollars and a definite cost per dollar increase in sales. With reference to the practical utilization of broadcasting by an advertiser and such specific and relevant problems as the method of procedure for the selection of stations, programs, management of artists, methods of preparing script, personnel and organization required, and methods of tabulation of returns, little if any information is given. It is characteristic of the writer's style in this particular volume to use the primer method of asking a question and then attempting to answer it. "Of course if you were an advertiser seeking good-will on the radio, what would you send through the microphone to entertain a million listeners and hold them spellbound on a series of wavelengths until the program concludes? Would you contract for the Goldman Band, Will Rogers, Irvin Cobb, or would you fink the name of your product with George Gershwin, Galli Curci, Al Jolson, a prize fight or Paul Whiteman's orchestra, or would you select an opera, etc., etc.?" One chapter is devoted to selecting the broadcasting station for the commercial program. Dunlap calls attention to the fact that the station used must have a good wavelength and that it should reach an area which constitutes a market for the type of product involved. The selection of broadcasting stations has become much more than a matter of merely selecting one with the best wavelength, covering the area desired. Many complex questions now enter such as chain affiliations, habitual program character and its effect in establishing a particular type of audience at different hours, transmission quality, conditions on the frequency to which the station is assigned, suitability to the particular type of program which the sponsor desires to present and numerous other factors, now habitual considerations when advertising agencies are called upon to select broadcasting stations for a particular client. It is obvious that Mr. Dunlap's role has been one of skillful and competent observer at the loud speaker rather than actual contact with the problems of managing directing and placing broadcast advertising features. He deals very fairly with his true subject, the returns obtained by radio advertisers, and the book is certainly enlightening to one interested in this subject. It falls short, however, of a complete study of radio advertising and a guide to the advertising manager who would use the medium of radio broadcasting.— E. H. F. • april, 1929 page 388 •