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Show Use of Wave Trap for Good Results Part Is Serviceable Even in Loop Receiver, Radio Expert Says. By JAMES H. CARROLL, Associate, Institute of Radio Engineers, In Radio World. From all qunrters of the compass come Inquiries, as to wave traps and their uses and as to what Is the best type of trap to use for good results. Evidently there Is a great Interest In this handy little apparatus, especially under present conditions ; and even when the air Is eventually cleared a wave trap still will be a good thing to have around. Take as an example the solenoid wave trap, as represented by the "WEB" model. There -are two main reasons theoretically theo-retically for the success of this kind of trap and one Is because of the solenoid winding which enables the electrical currents flowing through It to establish a more evenly balanced set of lines of force which concentrate themselves in the center of the tubing and upon the concentration point of the variable condenser. In this type of wave trap It has been discovered that this makes for efficiency and has a great deal to do with tuning. Micrometer adjustment of Interference Interfer-ence elimination Is necessary for rejector re-jector circuits. Therefore, when using a wave trap of, this variety the condenser con-denser plates will be pressed very Elowly or the operator will not trap out the unwanted station. This is a point in favor of such a trap. Wave traps of this type can be effectively ef-fectively used In many different places. If you have been unfortunate In obtaining good results with a wave trap you may not have used It In the right place. In other words, you may have Inserted it In your aerial circuit when It would give you the best results re-sults in your ground circuit or some other place, Instead. In the Aerial Circuit. Let us first try the aerial circuit. Disconnect the aerial from your set and connect It to one of the posts on your wave trap. With a short wire connect the other post of the trap to the aerial post of your set from whence you previously removed the aerial. This Is the simplest and most nsual use of a wave trap, and It Is a good one, but under certain conditions It will not prove the most effective. If by this method we do not succeed In perfectly eliminating an offending station on the lower wave lengths let cs try Inserting our trap In the ground circuit. This Is done In the same way except that we substitute the ground wire for the aerial wire. This means is especially recommended recommend-ed for efficient low wave elimination but reports show that It also works equally well with the highest wave lengths and that also by this method additional stations have been tuned with a wave trap of the design we are discussing. Now, If we are working with a loop, we can connect our trap In the grid circuit, the most approved method of eliminating Interference In such a case and the only way of using a wave trap with a loop set. First locate lo-cate your grid wire that goes to the tuning device In your set, either coll or condenser. Disconnect this wire at the point of contact with the grid post of the socket. Connect It to one end of a flexible wire about two feet long. Connect another piece of flexible flex-ible wire of the same length at the place from which you disconnected the other wire and run these two wires outside your set to your wave trap, attaching one wire to one post of the trap and the other to the other post of the trap. You are now ready to eliminate Interference. This method, meth-od, even if it is a little more troublesome trouble-some to try out, Is well worth while, because It will mhke any set selective. selec-tive. Another Means May Be Used. Another means we may use Is the aerial and ground shunt, which Is one of the oldest methods known and among the most popular. All that need to be done to use this method of Insulation Is to run a wire from the aerial post of the set without disconnecting discon-necting the aerial wire to one of the j.o.-ts of the wave trap. Then run another wire from the ground post of the set to the wave trap. Although no tuning can be done with a wave trap used In this way It functions as an excellent trapping system and stations sta-tions In the vicinity of the wt can be dominated by this means. Jio riot confuse a wave trap of this type villi an apparatus such as the reiilnilab short wave selector, which Is what the name Implies and not a wave trap. It fills a very definite function of Its own and can he used very satisfactorily In con pinei ion with B trap of the type we have selected BS the best. While our testing was fielnc done find before this article was completed, B h-tTer came to h.'ind from ri f;in sIlti-InL' sIlti-InL' liluiclf n Junior Kadlo I'.eg nsk-Iru: nsk-Iru: for practically the Information gl(ji In this text, ari'l anion;,' other t r : 1 1 UT J lll'I'lililtL' UK to lhllt hei-Hllie of the fr.ippei) Matlon when f Mas clip tured. probably I'gurllig that It re miiit'erl In tin trap raiiiiiliii; i"-i':inl 1 find healing Its wates a;:.i.' t o. walls In a futile effort o escape. Well, Junior, you have staggered us here as we haven't the slightest Idea as to what becomes of the invading station; our idea Is that perhaps, getting get-ting its nose or its tail pinched In the trap. It tears away on the trail of other prey in the form of sets not protected by a beneficent wave trap. The earliest form of trap of any kind known to history was a pit dug in the ground by the caveman in front of his cave apartment. This was covered by twigs, branches and grasses so that it looked like a solid surface. Along came the marauding mammoth, in search of meat to vary his vegetarian diet, and tumbled in with a crash that shook the row of caves and dislocated dis-located every aerial In miles. Then, all that remained for Sir. Caveman and his tribe was to squat around the trap and sing and howl in chorus until un-til they sang the threshing behemoth to death. In which case they became the partakers of meat. It is evident, then, that the Inventor of the wave trap modeled It upon this efficient device, de-vice, taking a hole, or a pit, as It were, enclosing It In hakellte, disguising dis-guising It with a solenoid winding and adding the pinching condenser that squeezes the Invading station until It howls for mercy. j |