Radio age (Jan-Dec 1924)

RADIO AGE for May, 1924 The Magazine of the Hour 19 Doubling The Usefulness of Your Condenser Converted Single Circuit Will Surprise You For Selectiveness and DX By BRAINARD FOOTE D kESPITE the persistent outcropping of this or that "new circuit" the simplest one of all continues to hold its place as the most popular. This is the single circuit tuner and it is without question the equal of any other onetube receiver when it comes to distance. Its chief failing is its serious interfering radiation and its annoying lack of selectiveness. Another drawback lies in the large variation of tickler coupling which is requisite on account of the varying absorption by the antenna with varying coupling between set and aerial as controlled by the series condenser. With all of these objections, its sensitivity and its simple control have maintained it at the head of the list. Lately there have been several substitute tuners advocated in its place, all of them involving the addition of a simple and untuned antenna coupling coil and a modification of the tuning circuit consisting in shunting the variable condenser across the outer coil of the vario-coupler. This plan is highly desirable for several reasons. In the first place, and most important, it gains most remarkable sharpness of tuning without the slightest loss of volume. Next, the removal of the antenna from the tuned circuit removes the absorbing influence of the antenna on regeneration. With fixed coupling between aerial and set, the regeneration control is almost the same for all wave lengths. Then again, the fact that the antenna circuit is not tuned means that the radiation from the set while tuning is a great deal less than before — although still present in some degree, it is true. PANEL VIEW Figure 1. Neat design and selective sensitivity marks this coupled circuit tuner. The inductance coil is tapped and the tuning condenser has plenty of "room" between dial settings on low wave lengths. The Two-Range Feature With all of this great gain, there is one objection which holds not only in the case of this converted coupled circuit receiver, but as a matter of fact in every case where the entire broadcast tuning range is covered by a fixed coil and a vari • 1 j i _3^ -TV # r '.< * i L 4I< •• nwuH ft. / — — '•-' "3 ■ .'2 8 -IHP 9 Jt.1 r '^!^^pH| |fc ■ ] ■■■■'■' --^J."^^ ■ ■ .. ASSEMBLED SET Figure 2. And it works as well as it looks. You can remodel your old single circuit set in a few moments, or if you'll like to make a new one, here's a suggested arrangement. able condenser. While the tuning is easily done on waves about 400 meters, and the stations do not seem to be crowded together seriously, on the lower wave lengths the case is far different. Operators of the Neutrodyne and other tuned R. F. receivers will agree with me when I say that there is not enough latitude in the movement of the variable condenser for low waves. This is due to the fact that the value of inductance is too great for easy tuning on low wave lengths, and because of this that I am suggesting a slight alteration which I know will be of untold benefit to you in your short wave reception — say between 200 and 360 meters. I am going to start off by telling you what can be done with a double range circuit and then to tell you later on how you can either build yourself such a set or modify your own single circuit receiver to give equally pleasing results. Figure 1 gives the panel view of the circuit in question — the three-circuit tuner entailing untuned antenna coupling coil, tuned secondary and tickler for regeneration. Let us start off first by moving the switch lever to the right, where the entire secondary winding of 80 turns is in shunt to the condenser; the 600-meter commercial stations come in at 85 on the left hand dial. The highest broadcast wave length, 546 meters, is that of KSD, and is tuned in 66. Coming down, we find WWT at 58, KYW at 62y2, WCAP at 44, WJZ at 40, WMAQ at 381/,, WOR