Radio broadcast .. (1922-30)

Record Details:

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A Good Four-Tube Receiver 901 upon the amount of regeneration used. The obvious thing to do is to combine some form of variable regeneration with stable radiofrequency amplification. If the r. f. amplifier is neutralized and the regeneration take place in the detector circuit, the result is an extremely sensitive, non-radiating receiver. In the more congested centers, the effect of the "bloopers" or radiating receivers is not becoming a menace, but is one, and most seriously interferes with satisfactory reception of broadcast programs. The set to be described herein presents nothing radical nor does it incorporate any wild or so-called new ideas. It is, on the contrary, merely an application of sound design principles in an endeavor to produce a receiver which would embody all the advantages of the neutrodyne plus those of the regenerative receiver and with none of the draw backs of either type. Certain definite requirements were laid out before development was started: 1. The receiver must, when using a 75-foot outdoor antenna give results equivalent to a good seven-tube super-heterodyne when operating on a loop, with respect to sensitivity, selectivity, quality of reproduction, ease of control and simplicity of assembly. 2. The set must employ a minimum number of tubes operating at maximum efficiency. 3. It must be non-radiating. 4. The equipment used must be as efficient as it is practically possible to make it. 5. The construction and assembly must be simple enough for any one to build. 6. The parts cost must be kept within reasonable limits. 7. An extensive course of "trouble-shooting" must be absolutely unnecessary. In other words, the set must work, if it is assembled properly, without trouble and experimenting on the part of the builder. The general design is shown in Figs. I and 2. U will be noticed that the mechanical require ments come up entirely to what was planned for it. As for results, with the set located in Chicago operated with a 75-foot out-door antenna, stations on either coast may be brought in with loud speaker volume on the four tubes while all the locals are operating. Practically all tests of the receiver were conducted in a location midway between WEBH and WQJ, located approximately one-half mile apart. It was entirely possible to bring WGY operating on 380 meters through WEBH operating on 360, with no interference and it was possible to bring several 440 meter stations through WQJ operating on 448 with only a slight amount of. back-ground interference. On the lower waves the selectivity was sufficient to separate KFNX, KFKX, WJJD, WTAY, and WTAS, all operating within a very narrow wave band. The selectivity was almost up to that of a seven-tube super-heterodyne and the volume with the outdoor antenna was equivalent to that obtained with the "super" on a loop. WHAT THE SET DOES ADDITIONAL tests were then made to •*» determine what the set would do on a 2o-foot indoor antenna, and most satisfactory results were obtained — stations throughout the country being brought in with ease and in the case of all the more powerful ones, with loud speaker volume. The set was also tested for radiation and it was found that with the detector oscillating and beating on a given station that the same station could be picked up on a super-heterodyne about 25 feet away with no evidence that the four-tube set was oscillating. The circuit employed consists of one stage of tuned r. f. amplification followed by a regenerative detector and two stages of audio amplification. The r. f. amplifier is neutralized to prevent oscillation and radiation, although where 199 tubes are used it is often FIG. 2 The "works" of the four-tube set built by Mr. Silver. Note the connection of the neutralizer to the tap off of the vario-coupler secondary coil. All the parts are mounted on the panel and no baseboard is used