Radio doings (Dec 1930-Jun1932)

February, 193 RADIO DOINGS Page Thirty-one /H CRT-WAVE PAGE The National SW-5 We have had many requests from short wave fans for the circuit diagram of the National SW-v It is given below, with data and notes on this highly efficient receiver. Engineered from the ground up for short-wave one-dial humless AC reception, the SW-5 has a sensitivity comparable with that of many multi-stage RF broadcast sets. The tuned radio frequency stage ahead of the regenerative detector is necessary if anything like worthwhile short wave reception is desired. The added sensitivity and selectivity of this stage brings the whispers up to audibility and permits spreading them out in the congested bands to avoid interference. In the design, every precaution has been taken to prevent energy losses in the radio frequency circuits, to provide smooth control of regeneration and in tuning, to eliminate all hum so that headphones may be used when desired. Amateurs have found that the SW-5 provides reception on their bands superior to that which they have heretofore obtained with their home-constructed and more or less hay-wire layouts. These receivers have been adopted for certain phases of commercial short wave work, which is strong evidence of their efficiency. Referring to the diagram, Cl and C2 are special 270-degree tuning condensers of 90 micro-microfarads capacity. C3 is a midget trimming condenser. It will be noted that this trimmer is not connected in the tuned circuit connected to the grid of the RF tube, but rather is in a separate coupled circuit, which permits of more exact ganging of the two tuning condensers for one-dial control. C4 is a 100 micro-microfarad mica condenser. C5 is a small coupling condenser. C6 1 mfd paper condenser. C7 is 100 to 250 mmfd. mica condenser. C8 is .5 mfd. paper condenser. C9, C10, Cll and C12 are .01 mfd mica condensers. Pi, Si. Tl represent the windings of the antenna input transformer. P2, S2, T2 are the windings of the detector transformer. Rl is a 350 ohm bias resistor. R2 is a 5 megohm grid leak. R3 is the audio bias resistor, 2000 ohms. R4 is the second audio bias resistor of 1000 ohms. R5 is the regeneration and volume control potentiometer, 50,000 ohms. R7, R8 and R9 represent the voltage divider, having a total resistance of 12,000 ohms, tapped at 3100 and 4100 ohms from the negative end. A careful study of the diagram and the values of the units will enable many experimenters, fans and amateurs to improve their shortwave reception. The antenna and inter-stage plug-in coils are identical. Phone Jack m red. fier filter Schematic diagram of Rational short wave receiver SW-?. A fine control set engineered for the highest efficiency in short The range of the four sets of coils is as follows: Black, 14 to 25 meters, 21.2 to 12.0 megacycles. Red, 23 to 41 meters, 13 to 7.33 megacycles. White, 38 to 70 meters, 7.9 to 4.3 megacycles. Green, 65 to 115 meters, 4.7 to 2.61 megacycles. The first broadcast stations to locate when learning to operate the set are the group in the 48-49 meter band. W9XF (Chicago), W9XAA ^(Chicago), W2XE and W3XAL (New York), W3XAU (Philadelphia), W8XK (Pittsburgh), and other Americans will be readily found near 90 on the dial when using the white coils. Messed in with them are HKT. Bogota, Columbia, and HRB in Honduras. The foreigners may be searched for after the operator is familiar with the operation of the set. VK2ME in Australia comes in at about 85 on the red coil, and G5SW, London, near 55 on the red. However, in going after the foreigners, one must take into consideration the time difference throughout the world and try at the proper hours. There's a little more to bringing in those elusive foreign short-wave broadcasters than merely sitting down to your receiver, flipping the filament switch and carelessly twiddling the dials. Yet, many a broadcast listener has been led to believe that it's just as easy as listening to a local program. Not only must the operator of a short-wave receiver exercise greater care in tuning in to a distant station, but he must use his judgment as to when to listen. All the tuning on earth won't bring in a station if it doesn't happen to be on the air. Matters become more complicated in this respect because of the difference of time between the location of the receiver and the transmitter. There's no doubt about it, a fellow's got to use his head when tuning in on the short waves. The list of shortwave broadcasters in the New 1931 RADIO DOINGS CALL BOOK is the most authoritative and latest which it has been possible to compile. Skip distance effects vary with wavelength, time of day, and the condition of the atmosphere. Therefore, divide your listening schedule something like this. 14 to about 20 meters, best from daybreak to about 2:00 p. m., and then fades out as darkness approaches: it is useless to listen below 20 meters after dark. 20 to 35 meters from 1:00 p. m. to about ten in the evening. 35 to 75 meters, best between twilight and daybreak. "Ham" Call Book Issued A call book listing the 19,000 "ham" radio stations has just been issued by the Radio Division of the Department of Commerce. The amateur stations are listed alphabetically by states and cities and call signals. .„„ The book also contains a list of the t e c h n i c a 1 and training school stations, experimental stations, relay broadcasting stations, visual broadcasting stations, the International Morse Code and conventional signals, a list of abbreviations used in radio communications, and a list of the nine radio districts with the headquarters of each. Copies of this book may be obtained directly from tube. dMectric. single the Radl° Division, Department of wave reception Commerce, Washington, D. C.