Radio Broadcast (May 1928-Apr 1929)

ShortWave Receiver A SHORT-WAVE RECEIVER FOR 11.2 TO 219 METERS Its construction is fully described in the article below, data for making the coils also being given. The three coils shown by the side of the receiver are for the 175, 80, and 20 meter ranges. A table on page 14 gives the number of turns for various frequency bands 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 (1 1.2 to 219 meters approximately) The receiver may be used with any audio amplifier system. It is completely shielded in a copper box iof" wide, 9J" deep, and 6" high. The copper sheet from which the box is made is tz" thick. All joints are soldered and the top opening of the box is reenforced with \" by \" by tV' 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 \" wide by tV 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 1 \ \" by tV 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 and regeneration controls and the output binding posts. Note that the copper box is not centered 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 connections to the antenna, A battery, and to the detector 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 ioj", by 85", by iV thick. As will be seen by reference to Fig. 1, the antenna is coupled to the antenna coil through a General Radio midget variable condenser of 15-mmfd. capacity, Q. 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, C3, is a Cardwell of 50 By Lloyd T. Goldsmith Col. E. H. Green Radio Research 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 he 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 intermediatefrequency amplifier. It will, on the other hand, be wonderfully sensitive for code reception. — The Editor. 31SV mmfd. capacity of the straight frequency-line type. The regeneration condenser, C2, is a National 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, C4, is a 100-mmfd. Sangamo across which is a Tobe 8-megohm grid leak, Ri. The detector tube is a ux-201-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 radiofrequency plate choke, L3, is a Samson No. 85 of 85 mh. inductance The audio-frequency choke, L4, in the positive B-battery lead is a SI®*55 Samson No. 3 of 3 henrys inductance. The audio + A -A FIG. I Circuit diagram of the short-wave receiver described in this article 13