Show I ammo 0 Au die ti P 5 I c 0 0 cl II AC e ecat cat catI I 1 i 90 V 4 Copyright Radio 1926 A Two Tube Wave Short Receiver Of all the th receivers submitted for tor forthe forthe the Judges approval In the Radio Broadcast Magazine WO contest for tor tora fora fora a short wave receiver that would not radiate not a single one of ot them could meet this latter requirement About fifteen receivers were select select- selected ed d d for tor consideration out of ot all those entered In tho contest Exhaustive e tests conducted at nt t 2 GY Gt the thc experimental experimental mental wave short station of ot Radio Broadcast showed bowed that all of ot the re- re receivers receivers re receivers submitted by contestants did radiate To determine those which radiated the l least ast the following tests were made At station 2 GY Gt a stand stand- standard standard ard Reinartz receiver recel Is In n use By keying the plate circuit of ot this re- re receiver receiver re receiver code was transmitted to nn- nn another an another other receiver In n the office of Radio nacHo Broadcast some yards away ny Later when a microphone was placed In the ground lead of ot the Reinartz speech was readily understandable atthe at atthe atthe the office The contest receivers were compared to this set Those which ra- ra radiated ra radiated as badly were at once elim elim- elimInated dim dim- eliminated mated It soon became apparent that not one of ot the surviving group of ot the contest receivers ers satisfied the con con- con of ot the contest With the per per- permission permission permission mission of ot the Judges Boyd noyd Phelps Phelp Prof Pro L A Zeh Leh Bouck G O 0 Furness Arthur H II L Lynch I Edgar n II Felix Dr Lawrence La Dunn Proto Prof J JH II 13 and Dr A Hoyt Taylor Ta lor and the designers of ot the receivers which came nearest to satisfying the conditions It was decided to award to the designer of ot the receiver which radiated the least and which was at nt the same time sensitive The receiver chosen for tor the thc award was designed ed by Frank C 0 Jones operator operator op- op orator of or of ot Berkeley Calif and Is shown In the schematic dla- dla diagram dia diagram gram In this receiver radiation Is practically eliminated It if due care Is taken In making the final balance adjustments ad- ad adjustments ad adjustments There Is nothing startling startling- startlingly ly ly new about It except that the thc principle principle principle of ot the Wheatstone bridge Is incorporated Incorporated In- In The Condensers In the article In Radio Broadcast Magazine photographs are given so that the would be constructor may approximate ap- ap approximate ap approximate proximate the layout of ot the original but as Mr Jones points out most amateurs will wish to use their own ideas In thIs tills matter The two van van- vari varl variable able condensers Cl and are of tip tip- ap proximately OIIn and mM respectively should prefer preter- preferably preferably ably be of ot the straight line frequency frequency type and should have low minimum capacity The balancing condenser 03 Is la a midget condenser of about capacity Once Ctt et this latter may moy be left lett alone and Is not considered a main control Our next consideration concerns concern the coils colis In the diagram LI Ll Is a flied fixed tickler coil coll coupled to the tuning In- In Inductance In Inductance while the antenna coil 12 which Is shown with an optional tuning condenser dotted across It Is mounted as far tar from the other coils as possible It Is recommended that two binding posts be arranged on a strIp of ot hard rubber so that this coil may be connected to them and yet be located outside the receiver some two feet or so away The center tapped coil coll Is a wound space-wound one with a 3 Inch diameter For the smaller coils colls No 10 d c c wire Is used while No 1 18 d c c Is recommended recommended mended for the larger ones The tickler tick tick- tickler tickler ler tolls colls are wound on Inch 2 diameter diameter eter cardboard forms torms these forms torms belag be- be beIng be being ing lag removed after the coil coll has been made rigid with a coating of collo collo- dion 13 consists of ot from 5 6 up to 30 turns and may be wound In the some same manner as The following tollo tables gives the turn numbers for forthe forthe forthe the various frequency bands Turns for Frequency Bands Bandt 33 aa a d s a 8 8 44 o eE-o o E-o a u Ao C o o t U oZ E-oZ t z U u d ea li 4 I 6 1730 IT 3 Apr A r nItO ll t-m t I a 8 T 7 9 65 13 0 41 d 1303 3 24 21 11 Tt 13 IS t l 21 U 43 13 12 no ao-no It 17 Apr Ayr By virtue of ot the fact tact that the thc 11 1 di- di diameter di diameter ameter of ot the tickler toll coll Is less than that of ot the toll coil It Is coupled to the former Is mounted concentrically within the latter and Is held beld there therewith therewith wIth thick thread The r f t choke coil coll may be pur pur- purchased purchased purchased chased or one may be wound on n a a Inch form torm honeycomb fashion with GO 50 turns of ot fine wire The grid con con- condenser condenser condenser denser should be the best obtainable obtainable and should have a capacity of approximately I |