Radio Digest (Oct 1923-July 1924)

RADIO DIGEST — Illustrated January 19, 192k TESTS SHOW HOW TO SHUT OUT CITY BROADCASTERS (.Continued from page 1) Radio world, but their use lias been limse of little experinu and because the "air" has not been so badly heretofore. But every in hunter, or "DX hound" as .ers have named him, will tell 3 the ether is crowded to the 1st now Classes of Wave Traps in Use Not so wiiii proper wave traps! The tuning Ueast selective) set can through troublesome interwhen equipped with any of the ective devices as the experiments Digest's technicians have proven. V 25 ;turn COIL SH0RTCIRCU1T SWITCH " 23PL. TO AERIAL BINDING POST ON SET Figure 1 — Series type of wave trap. Wave traps have numerous forms and applications. Some are directly connected in series with the antenna or even the ground lead, others are inductively coupled to some portion of the primary circuit, and then again a few traps are integral parts of the tuning unit of the receiving set. The Series Wave Trap One form of wave trap which is connected in series with the antenna or nd lead, is shown in Figure 1. This ronsists merely of a 25-turn honeycomb ■oil with a 23-plate (.0005 mfd.) variable :ondenser connected across it. The cost is low even though the most expensive type of condenser is purchased. A switch is provided so that the trap may be short-circuited when its use is aesirable. This is a very simple and inexpensive form and therefore presents the most attraction for the average fan. Parallel Type of Trap In the second illustration, Figure 2, is shown the style of wave trap in which* honeycomb coil or other coil inductance and condenser are connected in series, but with the resultant unit connected as a whole in parallel with the primary circuit of the receiving set. VT/AERlAl. with the smaller, 10-turn coil. The two -0-turn coils, wound also with number 18 or 16 wire, are really but one 40-turn coil which has been separated in the center to allow room for the winding of the 10turn coil. How to Make Inductive Type Procure a piece of cardboard, fiber or hard rubber tubing 3 inches in diameter by 3 inches long. On this, beginning %inch from the center, wind 10 turns of number IS double cotton or silk covered wire. On each side of the center coil (.winding in the same direction) wind 20 turns of the same kind of wire. Now connect the two outside coils in series, using one end of each of the two windings, and being sure to see that the turns all run in the same direction. Across the remaining two ends of these coils connect the .0005 mfd. variable condenser. The center winding should also run in the same direction as the outside windings, but its two terminals are connected respectively to the aerial lead-in itself and to the aerial binding post of the receiving set as shown in Figure 3. Influence in Tuning1 When, after having constructed and connected in one of the forms of wave traps described, the set is to be tuned, adjust your set as before but leave the trap variable condenser set at zero (no plates interleaving). In comes the favorite noisemaker, the one for which you've been "baiting your trap." Just turn the trap variable condenser over slowly from zero toward full capacity until you "catch" the offender. You will know this point by the absence of his interference. oo OO 20 TURNS -^SOD.C.C, 3T06E JO TURNS •20D.C.C, Figure 3 — Inductively coupled wave trap. Now tune your set for distance. The dials will not all register the familiar readings, but will be a little different on account of the influence of the added capacity and inductance of the wave trap. The information here given on the subject of wave traps will be supplemented next issue by H. J. Marx, who will give working drawings and detailed data on the making and operation of a most effective trap. CONTENTS Badlo Digest. Illustrated, Volume Vin, Number 2, published Chicago. Illinois, January 19, 192*. Published weekly by Radio Digest Publishing Company. 123 West Madison. Street. Chicago. Illinois. Subscription rates, yearly. Five Dollars; Foreign Postage One Dollar additional; single copies Ten Cents. Entered as second-class matter at the postorhce at Chicago, Illinois, under the Act of March. 3, 1879. 25TO30 TURN COIL I23PL OftERIAt RECEMNG SET Ogroonq "All the Live News of Radio" 1 to 7 Simple Three Tube Neutrodyne S What Is It We Call "Static" ? by Dr. A. Meissner 9 Operating and Trouble Finding, for new owners of standard receiving sets, Federal 59 and Grebe CR-14 11, 12, 13 An Evening at Home with the Listener In 14 Advance Programs for the Current Week 15, 16, 17 Radiophone Broadcasting Station Directory — Part II 18 Mlloplex X Percolates Even with a. Modification ' 19 Editorial; Indi-Gest; Condensed, Hy Dielectric/fv-, ,a ' / zo How Good Is Good Receptiop ? by E. T. Flewelhng 21 Simple Explanation of Radio for Everybody, Chapter IX, Part I— Audio Frequency Amplifies lion , by M. W. Thompson 23 How and Why of Super-Heterodyne Receiver, Chapter I— Fundamentals of the Circuit, by H. J. Marx 2S The Reader's View 26 Selective Three Tube Single Circuit Receiver, Part III— Operating Instructions, by Fred Grill . 27 New-Born Colt Plexy Number II, R.D.-lll 28 Flexible Single Circuit of Selectivity 29 Questions and Answers Radio Illustrated, a Page of Pictures ........................ 3Z -=GROUND Figure 2 — Parallel type of wave. trap. In this type, the tuned circuit acts as a by-pass to the ground for those wave lengths which interfere and are therefore to be eliminated. In this style of tiap, as with the first type considered, all that is needed is a good variable condenser and an inductance coil of the sizes specified before. Inductively Coupled Trap Undoubtedly the most efficient form of wave t;ap today is the inductively coupled ■-. In this style. Figure 3, a small inductance of about 10 turns of wire, number 18 or 16 preferred, is connected in es with the antenna lead of the set. On each side of this coil are two 20-turn coils connected in series with one another and a .0005 mfd. variable condenser, the two jer coils being inductively coupled Looking Ahead FOLLIES DEBUT ON AIR (Continued from page 1) died the program from the studio by means of a special sealed wire running from the newspaper plant. Taking part in the main feature of the evening — the offerings of the "Follies" stars — were Miss Patricia Salmon, the cowgirl yodeler "found" by newspapermen at the Dempsey-Gibbons fight in Shelby; Gilda Gray, principal of the "Follies;" Elsa Peterson, Alexander Gray, Evelyn Law, singers; Virginia King, violinist: J'mmy Hussey, comedian, and Andre Tomes. Yvette and her New York Syncopators, playing at a third theater in the city, ished further pep for the program, the early part of which was made up by such stais as Wendell Hall. Herbie Mintz, the odians and a score of others. William J Clark, Radio editor of the Arnerr toned the long program with a word of ap-eciation to the followers of the new studio. Neutrodyne Sounds Difficult, but It Will Be Easy to make the five-tube Hazeltine Neutrodyne H. J. Marx will begin to describe next issue. The instructions are simplified but very detailed and should permit the greenest novice to understand clearly. The article will be in two parts, the second coming week after next. Dr. A. Meissner, the World Known Authority, Knows Static. — If you knew where it was "made" and how, would it help you? Read Dr. Meissner's article next week. Superheterodynes Are the Latest Step in Radio Do you want to take the last step? jli**16 inrormation H J Marx will give next week on oscillators and super audible transformers. Another circuit will be given, too. The articles this week and next are breaking the ground, so to speak, for Mr. Marx' real Superheterodyne construction series. How to Operate Your Set and Find Trouble, that is, when trouble arises, is clearly described in the new feature, "Operating and Trouble Shooting." See pages 1 I, 12 and 13. Two more sets will be given next issue. Cutting Out Locals and Getting Distance isn't half as hard as you think. Build a wave trap a real one. How? H. J. Marx will give complete details next week so you can put one together. What Else to Expect Next Week — M. W. Thompson will continue his discussion of audio frequency amplifiers; Fred Grill will do a Presto Chango showing how to turn your set into a Grill Hook-Up ; Lots of other well-known Radio writers will tell you lots of other valuable things. 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 Publisher Radio Digest, 123 West Madison St., Chicane, Illinois. Please And enclosed check M. O. tor Fly* Dollars (Six. Foreign) for One Year's Subscription to Radio Digest. Illustrated. Nairn Address Cltt 8tato. The Dependable Radio Receiver FADA "ONE SIXTY" with the NEUTRODYNE CIRCUIT The FADA "One Sixty" is the four-tube Neutrodyne radio receiver that in selectivity, volume, distance and clarity equals the best results of any five-tube set of any type or make. Owners say, "If we don't get 'em on the loud speaker, we don't count 'em." Consistent performance on loud speaker from stations 1500 to 2000 miles away and sometimes much further. Price $120 at dealers Extra for tubes, batteries and 'phones F. A. D. ANDREA, Inc. 1581 Jerome Ave., New York City Quick Positive ■ Connections* Union Radio Tip Jacks (Patent Pending) Price 25c Just what you want when building your own set or experimenting with new hook-ups. Not only give positive electrical contact, they improve the appearance of your set. Two sizes for all mountings. Standard Type A for panels up to K-inch thickness, Special Type B for panels, cabinet walls and partitions from A to Vt inch thickness. Will firmly grip all wires from No. 11 to 24 B & S gauge, and can be reamed to pass and hold antenna wire, battery leads, loading coils and vacuum tube lugs. No parts to lose, chip or deteriorate. All parts heavily nickeled. Price 25c OTHER GUARANTEED UNION RADIO PARTS Dial adjusters for minute variations in capacities of variable condensers. Price 60c Tube sockets of molded condensite highly polished. Phosphor Bronze contact springs. Reinforced bayonet slot prevents breakage. Accommodates all standard tubes. Price 70c Should your favorite Radio Store not carry Union Radio Tip Jacks and Guaranteed Parts send your order direct to us, also write for your copy of "The Union Radio Catalogue 'H.' " RETAILERS AND WHOLESALERS Samples of our guaranteed, reasonably priced "Quality Products" sent on request. Our terms and trade discounts ar« liberal. Write for our proposition. UNION-RADIO-CORPORATION ^OO-MT. PLEASANTAVEN U E,~ NEV^AAK-NJ VIEW YORK-OFFICE — n6-WEST-32=-STREEE m