Radio Broadcast (May 1928-Apr 1929)

A RECEIVER OF MODERli DESIGH FOR THE DX FAX More Data on the Sargent-Rayment placed in a single stage compartment for measurement. It was observed that with constant coupling maintained for each coil, the amplification Obtained increased with decreases in coil size, due to a reduction in shielding absorption. The most satisfactory coil of the various types tested consisted of 72 turns of No. 25 enamelled wire wound upon a bakelite tube 25" in diameter, threaded 32 turns to the inch. When measured unshielded, this coil actually was inferior to a larger type which, also wound upon a 2§" tube, consisted of 80 turns of No. 20 enamelled wire, threaded 20 turns per inch. This larger coil, being affected to a much more marked degree by the presence of the shielding than was the smaller coil, actually delivered lower amplification in practise. This is indicated by the curves, Fig. 2, showing the amplification obtained with four different values of screengrid voltage when using the larger coil with a primary consisting of 35 turns of No. 34 d.c.c. wire slipped into the secondary at the filament end of the latter. Amplification with 45 volts on the screen grid ranges from 17. to 26.5 between 550 and 1450 kilocycles, with selectivity varying 3.9 to 1.2] for the different frequencies. The curve of Fig. 3 taken upon the smaller coil with a 25-turn primary shows a considerable improvement in amplification over the larger coil, and a very appreciable improvement in selectivity as indicated by the selectivity figures appearing in the curve. (These selectivity figures represent the ratio of amplification of the desired signal to the amplification of another signal 10 kilocycles off resonance, and to the engineer the merit of the stage represented in Fig. 3 will be appreciated as being quite high.) HOW SENSITIVITY IS OBTAINED TTO THE average reader, the values of am*■ plification per stage shown in Fig. 3 may seem quite low, but it must be borne in mind that in designing the Sargent-Rayment receiver AT THE time the article entitled "The Z_\ Sargent-Rayment Seven Receiver" was prepared for October, 1928, Radio Broadcast, the writer, as a result of testing a model receiver attendant upon the preparation of his article, had become firmly convinced that this receiver was an unusual example of a fine kit, and that, in short, it would be heard from in no uncertain terms once a number had been built. Circumstances have since proven that the silent prophet is not always unhonored in his own country. Believing that the comments of some experienced experimenters who have built and tested the set may be of interest, as well as a bit of additional engineering data and a few timely operating suggestions, this, the writer's second article upon the Sargent-Rayment Seven Receiver, has been prepared. Extended experience with western conditions on the part of the designers of this receiver had effectively convinced them of the necessity of a far more selective set than would in all probability ever be developed in the East, due to the peculiarities of western reception conditions. In consequence, it would seem that if the Sargent-Rayment receiver were capable of giving a good account of itself on the West Coast, it would certainly be able to do so in any other location in the United States. Such is actually the case. As an example of results obtained from a typical Sargent-Rayment set, a report received from Lloyd Breck, 1 10 Pacific Avenue, Piedmont, California, is most interesting. In the course of two evenings' tuning, Mr. Breck was able to tune in a total of 1 16 stations upon the receiver he had built. Out of the total of 1 16 stations, 44 •were located in the East, and Mr. Breck's log included cyj and cya of Mexico City, kfqd of Anchorage, Alaska, khgu of Honolulu, Hawaii, and pwx of Havana, Cuba. The log is interesting, for there are only approximately 100 transmission channels in the broadcast band, and the reception of 116 stations meant that several transmission channels were heard from twice! Turning from Mr. Breck's results, the comments of F. Edwin Schmitt, of New York City, upon the performance of a Sargent-Rayment located at White Plains, New York are inter CT'HE Sargent-Rayment receiver was first ■*■ described in our October, 1928, issue. This article gives additional operating notes and other comments which are sure to interest those who have built the set and probably will be of interest to those who may now be planning to build one. — The Editor. esting as coming from the opposite coast. Mr. Schmitt reports that between the hours of 8:00 and 12:00 p. m. on an evening late in October, one station in Portland, Oregon, one in Seattle, Washington, one in San Diego, California, three in Los Angeles, one in Denver, one in Fort Worth and many closer by were heard with excellent volume on the loud speaker through the barrage of stations located in and about New York City. These comments, together with reports of average logging of from 50 to 100 stations in an evening from many different builders, indicate that the receiver is evidently adequately selective for present-day conditions. REGARDING COIL DESIGN IN FIGS. 2 and 3 are some interesting amplification curves made upon several typical r.f. stages tested in the development of the SargentRayment receiver. In order to determine the most satisfactory type of coil for the general type of mechanical assembly which seemed desirable, a family of coils, each of approximately the same inductance, were constructed and 197