ESTABLISHED 1917 10c in U.S.A. and Canada February, 1937 1/8 in he Uni'cd Kingdom; 2/- in Australasia No. 21 0 New 100 -T's in a 3 Band Transmitter Direct Reading Percentage Modulation, Instantaneous Remote Controlled QSY A Low Cost 913 Midget Oscilloscopc Greater Radiophone Intelligibility www.americanradiohistory.com HEAVY DUTY Will Give Your Rig MORE DX APPEAL! Equip your rig with Taylor heat -tested Carbon Anode Tubes and contact those elusive DX stations Taylor's Combined you haven't been able to land! The extra power of Catalog and Hand- these custom -built tubes will give your xmtr an book, FREE, tells you entirely new "personality." And man O' man how how to more you will slay 'em! For medium power, try a pair of put DX Taylor T -55's ... the fastest selling amateur tubes appeal in your rig. on the market ... each with 55 watt plate dissipa- Send for it or get it tion has a rated input of 225 watts. For real wallop at your favorite dis- adapt your rig to Taylor T -155's or Taylor T -200's tributors! and get a rated input of from 600 to 700 watts! More Watts Per Dollar" TAYLOR TUBES, INC. 2341 WABANSIA AVENUE CHICAGO, ILL. www.americanradiohistory.com RADIO MFG. ENGINEERS BELIEVE IN PROGRESS Look Inside if You Are After Facts. FIRST All component parts used in the manufacture of the RME -69 receiver must be well chosen and indi- vidually tested prior to installation in the receiver. NEXT The placement of parts for electrical efficiency and highest gain is a vital step in the design of this communication type receiver. THEN The workmanship, which high quality instruments display, readily discloses the methods employed in their manufacture. FINALLY The inspection given each RME -69 receiver before shipment leaves nothing to guess -work. It is pains- taking and extremely thorough. Look Inside and be Convinced of the Facts. BULLETIN 69 IS AVAILABLE FOR THE ASKING. RADIO MFG. 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Entered as second -class matter February 6, 1936, at the postoflice at Los Angeles, Calif., under the Act of March 3, 1879. 5 www.americanradiohistory.com Would you work for 6c AN HOUR? One amateur writes in that in designing, laying out, and cutting his two an- tenna systems, "THE 'RADIO' ANTENNA HANDBOOK" saved him over 8 hours. That is a pretty good return on a $0.50 investment, unless one figures his time worth only $0.06 an hour. If you figure your time worth more than that amount, you need ... "THE `RADIO' ANTENNA HANDBOOK" The " 'Radio' Antenna Handbook" is not just a reprint of various magazine articles. 90% of it has never appeared in any magazine. It was written from start to finish as the only complete book of its kind on antenna theory and practice. It is full of diagrams, tables of lengths for all frequencies, dope on all useful directive arrays, and a complete discussion of noise -reducing receiv- ing antennas. It is chock full of many new and useful wrinkles which are real scoops. U.S.A. and Canada 50c Elsewhere 60c At all good radio parts dealers or direct from us by mail, postpaid. DEALERS: Write for trade prices. NO STATION IS BETTER THAN ITS ANTENNA RADIO, Ltd., 7460 Beverly Blvd., Los Angeles, Calif. Please send me copies. ANTENNA Enclosed find $ in full payment. [50c in U.S.A. and Canada (Canadian postal notes acceptable); 2/6 in United HANDBOOK Kingdom (British postal notes and cheques on London acceptable at par); else- where, 60c, U.S.A. funds.] No stamps, please, unless other means of remittance are not available. Name-- ... - - -- -- Address 6City and State www.americanradiohistory.com THE WORLDWIDE TECHNICAL AUTHORITY OF AMATEUR. SHORT WAVE. AND EXPERIMENTAL RADIO i The publishers assume no responsibility, for statements made herein by con- tributors and correspondents, nor does publication indicate approval thereof. No. 216 February, 1937 CONTENTS Audio Selectivity with "Selectophones"-F. Malcolm Gager 8 A Truly Portable Receiver -John Hurrtoon, W9KJY - 12 The New ACR -175 Superheterodyne - 17 A Practical, Low Cost Oscilloscope - 19 A Neon Bulb Overmodulation Indicator- George W. Ewing, W6GM 22 U.H.F. Concentric Line Feeders -E. H. Conklin, W9FM - - 24 A Multi -purpose Frequency Meter -John Gluck. W8MYB 26 29 Measuring Audio Power - - - - - More Intelligible Radiotelephony -Ray Dawley, W6DHG - 30 Stabilizing the S.S. Superheterodyne-Charles D. Perrine, Jr., W6CUH 34 The Open Forum 37 What's New 39 42 Postscripts and Announcements - - - - Ten Cents Per Foot -Carlos S.