Radio Broadcast (May-Oct 1926)

268 RADIO BROADCAST ADVERTISER K ESTER Rosin Core RadioS^mm Sure & is Safe and Simple Approved by Radio Engineers A Genuine Solder Chicago Solder Company 4222 WrightwoodAve., Chicago, U.S. A. Originators and World's Largest Manufacturers of Self Fluxing Solder YOUR DEALER CAN SUPPLY YOU This is a good time to subscribe for RADIO BROADCAST Through your dealer or direct, by the year only $4.00 DOUBLEDAY, PAGE & CO. GARDEN CITY, NEW YORK MORE PROFITS for the PROFESSIONAL SET BUILDER XA/E have an unusually interesting * * proposition to make to the man who is now building (or has the ability to build) radio receiving sets for resale. This is a real opportunity. Write today for full information. Gearhart-Schlueter Radio Corp. 716 Vooi'inan Ave. Fresno, California How a British Fan Made Coils ception of the B. B. C's hong' Suitable for Re' Broadcaster PRIMARY THE popularity of the Roberts circuit in Great Britain is steadily increasing, and it is probable that far more sets of this type would be constructed if suitable long-wave coils were available. England's principal broadcasting station, that located at Daventry and known as s xx, transmits with a frequency of 187 kc. (1600 meters), which is far above the upper wavelength limit of the standard Roberts coils. In addition to Daventry, there are many other European broadcasting stations transmitting on even lower frequencies (longer wavelengths) than Daventry, and the average British fan is not content unless he is able to receive these long-wave broadcasters as well as those employing the shorter waves. This is essentially the reason why the Roberts has not gained even more supporters over here in Europe than it has done. There are extremely few factory made receivers on the market that are not capable of at least picking up Daventry, this being accomplished, in many cases, by means of simple loading coils. For nearly a year now, the author has been experimenting with the SECONDARY selves almost exclusively to listening to this station. DATA ON THE COILS ' I 'HE ordinary three-circuit tuner fitted A with honeycomb coils is easily changed to another waveband, but with circuits like the Roberts and the Browning-Drake, things are far more difficult. Nevertheless, the writer obtained very excellent results in adapting the Roberts for the longer waves. Solenoid coils wound with wire of the usual gauges were out of the question, on account of their size. The only way out of the difficulty seemed to lie in the utilization of multi-layer coils wound with fine wire. These were wound on a machine such astheone shown in the Radio Broadcast of February, 1925, and the number of turns equalled about five times the number employed in the standard Roberts .coils. Fig. 1 shows the antenna coil; on the left is the primary, and on the right, the secondary. These two coils are separated by a strip of hard rubber about one quarter of an inch thick. Both coils are clamped to an upright strip of ANTENNA COIL FIG. I Roberts, and much interesting data has been gathered. During these experiments, to permit rapid changes with a minimum of trouble, a simple breadboard layout was employed. On the usual broadcasting wavelengths, which are almost identical to those employed by the American broadcasting stations, very excellent results have been obtained. When conditions have been favorable, broadcasting from American stations has been heard with perfect clarity. As most readers are aware, broadcasting in Europe is at present in a very bad state. Considerable interference is experienced through new stations opening up on frequencies which are already being used by other stations close at hand, and the constant heterodyning is the bane of the DX fans' existence. Up to the present time, the Bureau established at Geneva to look into radio matters, has been unable to improve matters to any great extent. rhe Daventry station, fortunately, has been little affected by other stations, and many listeners in Europe confine them "A Tested and approved by Radio Broadcast -ir hard rubber, the latter being fixed to the baseboard by a metal bracket. The radio frequency transformer is shown in Fig. 2 (page 276). Again the NP coil and the secondary are separated by a thin hard rubber strip, and both are attached to the upright. The tickler coil is shown lying in the foreground. It was arranged to swing parallel to the secondary. The NP coil is tapped at the center, according to latest practice. As the wire used for these coils was very thin (about 30 gauge), no very startling results were expected, especially as the layers of the coils were close together. But when the set was switched on, the writer was agreeably surprised. When receiving Daventry, about 180 miles away, the volume was far greater than when receiving the nearest station, Manchester, 2 zy, about seventy miles away. Interference was absent, and only a faint whisper of Morse was heard at very rare intervals. Other long-wave stations, for {Continued on page 276)