Radio Broadcast (May 1928-Apr 1929)

JULY, 1928 A RECEIVER FOR SHORT-WAVE BROADCAST RECEPTION 169 The back panel, seen in the illustrations, should also be assembled separately with the antenna and ground binding posts, the antenna input choke, Li, the Yaxley cable plug connector and the audio transformers, and as much work accomplished on the separate units as possible before the final assembly. It will also be noted that the battery leads from the Yaxley connector to the audio transformers are cabled in soft wire and laced together with ordinary string. A careful application of shellac to this cable will stiffen it and make a neat appearance. The other assembly details are made sufficiently clear, we believe, in the photographs and the wiring diagram, Fig. 2. OPERATION THE operation of the receiver is very simple. With suitable tubes inserted in the sockets and with the battery voltages in the circuit diagram applied, one of the coils may be placed in the socket. With the regeneration condenser, marked "Volume," all the way out, the filament rheostat is turned up to about half brilliancy. Then, advancing the "Volume" condenser to a certain point, the detector tube should go intooscillation with a soft "thud," accompanied by a considerable hissing and increase in static. Should the tube fail to oscillate with the volume condenser fully advanced, the -filament rheostat should be turned up further. In the event that it should go into oscillation sharply or with disagreeable noises, it should Jje retarded to the point where oscillation can be accomplished with the soft "thud" mentioned. After oscillation is obtained, the wave band covered by the coil may be swept with the tuning condenser, always simultaneously manipulating the volume condenser in such, a way as to keep the tube just on the verge of oscillation. On passing a broadcast signal, a distinct heterodyne whistle will be heard, which may be chopped up somewhat by the modulation carried by the signal. After locating the heterodyne point of the broadcaster, the "Volume" condenser is retarded somewhat until the tube is just out of oscillation. The setting of the tuning condenser is then corrected for maximum signal strength and it will then be found that the volume control can be advanced with some increase in signal strength up to the oscillating point of the tube. In order to facilitate the location of stations whose wavelengths are known, the tuning chart shown in Fig. 1, has been prepared. It should be understood that this chart will vary somewhat with individual receivers due to small variations in coil and condenser characteristics as well as tube characteristics and wiring leads, but at any rate it will give those not familiar with the short wavelength stations a very definite idea of where to look for the experimental broadcasting station in which one is interested. LIST OF PARTS THE list of parts used in the construction of model illustrated here is given below. Other parts electrically and mechanically similar may be used, of course. It is not advisable to attempt the construction of the coils. The Aero kit comes as a unit, and at the present date it seems possible that the complete list of parts may be sold by the Aero Products company. Readers may obtain the manufacturer's constructional data and blueprints by writing to Radio Broadcast. U U Lj, L4 (1) Aero International Foundation Unit, complete with tube sockets and grid-leak mount. L5 (3) Aero No. 60 choke coil. Aero International Coil Kit. Naval, Transoceanic, Time Signals --■ 10-40 kc. Army, Navy, Gov't. 40-120 kc. Marine and Aircraft 120-153 kc. 10 20 30 -40 50 60 70 80 90 100 Government, etc. 153-285 kc. Coastal and Marine 285-500 kc. Aircraft and safety of Life 500-550 kc. Broadcasting 550-1500 kc. Amateur 1500-2000 kc.-— Point to Point, Relay Broadcasting.etc.-2000-3500 kc. Amateur 3500-4000 kc 200 300 -2000 3000 -4000 Miscellaneous: Pointto Point, Govt., Public Toll and Relay Broadcasting 4000-7000 kc. 5000 6000 7000 8000 9000 Miscellaneous J 10,000 8000-14,000 kc. Amateur 7000-8000 kc. < Amateur 14,000-16,000 kc.- Experimental 16,006-56,000 kc:"" Amateur 56,000-64,000 kcExperimental 20,000 30,000 40,000 50,000 60,000 70,000 < Radio Beacons 300 kc. Radio Compass 375 kc. KDKA 4760 kc. k WLW 5760 kc. 2XAF9150 kc. HI WHERE THE SHORT-WAVE BROADCASTS MAY BE FOUND This chart shows the allocation of wavelengths from 10 to 70,000 kilocycles; the portions of the spectrum set apart for short-wave relay broadcasting and amateur work are clearly indicated c3 (0 Amsco 140-mmfd. short-wave con (1) Yaxley 7-prong plate. denser. (2) Binding posts (Antenna & Gnd.). c4 (0 Amsco2 50-mmfd. short-wave con (2) Carter tip-jacks. denser. (2) National dials.. Ci, Cs (2) Carter .005 fixed condenser. c6 (0 Carter .0001 fixed condenser. Accessories c2 (') Carter .00015 fixed condenser. c7 (>) Carter .001 fixed condenser. (0 Yaxley cable connector R (0 Yaxley 10-ohm fixed resistor. VT 1 cx-322 tube. Ri (1) Yaxley 1 5-ohm fixed resistor. VTi, VT2 (2) cx-301-A tube R3 & S (>) Yaxley 20-ohm No. 520 rheostat VT3 (t) cx-3 12-A tube. with switch and knob. (1) 6-voIt storage battery. R2 (■) 7-megohm grid-leak. (1) pair Trimm head phones (or loud R4 (0 Yaxley i-ohm fixed resistor. speaker). T, Ti (2) Silver Marshal No. 240 audio (0 o-volt C. battery. transformers. B-battery supplying 135 volts.