Separating the Local Stations

Radio Record, Volume IV, Issue 47, 5 June 1931, Page 17

Separating the Local Stations

A Simple ‘Wavetrap For Crystal Sets WING to an unforeseen demand, we have sold completely out of the issue of May 22, which contained a description of a simple wave-trap, and we have been asked to repeat the description. Here are the particulars :- The materials needed are one vari-

Theoretical Diagram. able condenser, capacity .0005, #1b No. 26 enamelled copper wire, 1 three-inch length of cardboard former, 2in. in diameter, 2 terminals, 1 crocodile clip, baseboard 4in. x 5in., and panel (wood or ebonite) 4in. x 5in. Winding the Coil. HE coil consists of 70 turns of No. 26 enamelled wire, close wound, and tapped every . tenth turn, making six tappings in all.

Commence winding operations by piercing two small holes, about tin. apart, with a bradawl or knitting needle, about din. from che end of the coil. Thread the wire through these holes, leaving two or three inches for connecting purposes, and wind on ten turns. At the tenth, keeping the wiretaut, make a twist in the wire, forming a small loop about din. long.. Proceed thus, making a tapping at every tenth turn, until the 70 turns are wound on. The seventieth turn is, of course, not tapped, but the wire is threaded through two small hoies similar to those used at the beginning, and broken off, again leaving two or three inches for connecting purposes, At each tapping scrape the loop of wire bare of enamel, The coil is now complete, and may be mounted on the baseboard, either upright by means of brackets or on its side, fastened with two wood screws to the baseboard. Completing the Trap. HE condenser and terminals may now be mounted on the panel, and the latter screwed to the baseboard. fiverything is now ready for wiring up. This may be performed with the aid of the layout diagram, or by follow- ing these instructions. A piece of flexible wire is attached to the terminal on the left, and a crocodile clip fastened to its free end. This clip is taken to the most suitable tapping, to be determined by experiment. One end of the coil is taken to one terminal of the variable condenser, and the other end to the other terminal. A wire is then run from one of the condenser terminals-either is suitableto the terminal mounted on the right of the panel. The trap is now ready for operation, _ Using the Wavetrap. AKT .the aerial off the receiver and attach to the left-hand terminal of the trap. Join with a length of wire the right-hand terminal and the aerial terminal of the receiver. Now tune to the loudest. point of the station it is desired to eliminate. Then, by varying the wavetrap condenser and attaching the clip to different tappings in turn, a position will be found where the station signals fade into inaudibility. The trap is then left so adjusted, and the wanted station tuned in.