Radio broadcast .. (1922-30)

A SHORT-WAVE RECEIVER FOR ii.i TO 119 METERS THIS article describes the construction of a single-tube receiver and coils to go with it to cover the frequency band between 1.37 and 26.7 megacycles (11.2 to 219 meters approxi- mately) .The receiver may be used with any audio amplifier system. It is completely shielded in a copper box ioj' wide, 9!" deep, and 6" high. The copper sheet from which the box is made is h" thick. All joints are soldered and the top opening of the box is reenforced with \" by \" by ,',," angle brass which is soldered to the copper. Holes are drilled in the angle brass for \" 8-32 machine screws with which to fasten on the cover. The screws are soldered into the angle brass. The cover is of sheet copper reenforced at the edges and center with a strip of brass i" wide by T V' thick. Holes are drilled in the strip around the edge of the cover to allow the cover to fit down on the angle brass where it is tightly held by hexagonal nuts. Although it takes a few moments to remove and replace the cover when changing coils, this method of shielding has been found to be very complete and mechanically strong. The copper box is screwed to a 10" by 11J" by A" wood baseboard to which is also fastened by three wood screws the 7" by 12" bakelite panel. The only objects on the panel are the tuning agd regeneration controls and the output bind- ing posts. Note that the copper box is not cen- tered behind the baseboard but is set in \" from the left-hand edge of the panel in order to allow room for the output binding posts at the right. At the rear of the set there is a bakelite strip on which are mounted four binding posts for con- nections to the antenna, A battery, and to the de- tector positive terminal of the B battery. The three battery wires go into the copper box through one hole and the antenna lead through another. Most of the parts are mounted on an inside baseboard loj", by 8^", by A" thick. As will be seen by reference to Fig. I, the an- tenna is coupled to the antenna coil through a General Radio midget variable condenser of 15-mmfd. capacity, C,. A General Radio coil mounting holds the plug-in coils and is spaced a generous distance from the sides of the box. The tuning condenser, C 3 , is a Cardwell of 50- By Lloyd T. Goldsmith Col. E. H. Green Radio Rnrarch A "Super" for Code Work THE short-wave receiver described in this article has been designed for use with any ordinary audio amplifier, and when so used, will be found extremely sensitive, especially for code reception. The main purpose for its design, however, is its adaptation to the super-heterodyne unit described on the pages following those devoted to the present article. The super-heterodyne combination will not be satisfactory for short-wave phone reception due to the peaked characteristics of the intermediate- frequency amplifier. It will, on the other hand, be wonderfully sensitive for code reception. — THE EDITOR. 7 Ant. mmfd. capacity of the straight frequency-line type. The regeneration condenser, C 2 , is a Na- tional of 250-mmfd. capacity. The latter two condensers are mounted directly on the copper box and bakelite panel. Each is provided with a 4" National Velvet vernier dial. The grid condenser, C 4 , is a loo-mmfd. San- gamo across which is a Tobe 8-megohm grid leak, Ri. The detector tube is a UX-2OI-A and fits in a General Radio ux type socket mounted on a General Radio rubber cushion to absorb shocks and reduce noises. The leads to the socket are of flexible rubber-covered wire. The radio- frequency plate choke, U, is a Samson No. 85 of 85 tnh. inductance The audio-frequency choke, U, in the positive B-battery lead is a Samson No. } of 3 henrys inductance. The audio- ~l - I A FIG. I Circuit diagram of the short-wave receiver described in this article 13