Radio Digest (Oct 1923-July 1924)

October 20, 1923 RADIO DIGEST — Illustrated TWO WEIGHTY EVENTS IN AIR WORLD Sees Radio's Greatest Problem as Interference Caused by Re-radiation Howard Campbell, WW J Engineer, Says Corrective Measures to End "Bedlam" Must Be Taken If Broadcasting Is to Be Advanced tc ; {By Howard E. Campbell, Chief Radio Engineer, The Detroit News, WW J.) What place Is held today in the United States by regenerative detector receiving seta? Why is the use of regenerative detector receiving sets prohibited by law in England? It is estimated that three-fourths of all vacuum tube receiving sets in use today in the United States operate on the regenerative detector principle. There are more of these sets in operation than there are crystal detector sets. Why? Because at a relatively small expense the old crystal detector set can be rebuilt or replaced by a single-tube outfit which will enable the Radio amateur to hear stations from ten to twenty times as far distant. Because the idea of making a single tube perform the double duty of detector or rectifier and amplifier appealed almost universally to the shrewd American public. With the advent of vacuum tube Radio telegraph transmitting sets, code signals were sent in "CW," which is an abbreviaion of "continuous waves" of Radio freuency. Crystal detector sets could not distinguish these modern signals, but a regenerative tube detector can; hence its popularity with amateur Radio telegraphers. Cause Interference These statements answer to a certain extent the first question, but there is another side to the question which is demanding universal attention. Simple as these regenerative sets are, they have a characteristic fault. In regeneration they act as miniature transmitters and send out into space an interference during the entire time they are in operation which is picked up by other receiving sets within a radius of from two or three city blocks to eighteen or twenty miles, depending on the circuits used in the regenerative receiver interfering and the sensitiveness of the sets picking up the interference. It one set does this, hundreds and thousands of them in a large city generate a veritable bedlam of interference and affect each other and every other type of receiving set, from the cheap crystal outfit to the thousand dollar six to nine-tube outfit This interference is a hundred times more extensive and dangerous to the future development of the art than most Radio enthusiasts realize. The average' experienced operator of such a set will tell you that he never allows his regenerative tube to oscillate, and therefore does not retransmit or send out interference. Just Consider — the essential features necessary to make an audio frequency transformer a good one — High Amplification. Minimum Distortion. Low Inter stage Linkage. Convenient Mounting. Compactness. Cotoco transformers make these ideal features facts. And the finish will surely please you. "Built First to Last" $5.00 At Your Dealer's PACIFIC COAST BRANCH: 329 Union League Bids. LOS ANGELES COTO-COIL CO. PROVIDENCE To every Radiophan the name of Dr. Lc? OeForest is one to conjure with, but the news that he has sold his holdings in the DeForest Radio Telephone and Telegraph Company need not worry the Radio world, for he will remain with the new owners as consulting engineer. In the circle are, from left to right, Dr. DeForest signing the transfer documents, J. F. McNamara, of the Metropolitan Trust Co., and Edward H. Jewett, head of the purchasing group. To the right are Officers Tamburino and Pickerill of the Leviathan, holding copies of messages sent and received during a recent trip. In all they were 4,000 — a record-breaking number © K. & H. He means that he has passed the experimental or amateur stage where the tube "spills" or oscillates violently in his crude attempts at tuning and does not send out those disagreeable whining sounds which we all know so well. All Tubes Oscillate It will, therefore, come as a distinct shock to such enthusiasts to be told by Radio engineers that no tube will re generate without oscillating, and that unless he makes adequate provision In his circuit to prevent retranamission, his set will send out a constant interfering wave of noticeable intensity even while it is considered stably adjusted to receive a program from a certain station. This interference is very sharp; that is, it covers a very small band of frequencies, but. (Continued on page 8) THE 1923 RADIO SENSATION Never before in the history of Radio has a set of the quality and performance of the Michigan Midget been offered at anything like the price. No longer is it necessary to buy parts and build your own set and save money. Michigan "Midget" has done that for you. It puts a long range, high-grade radio receiving set within the reach of everybody's pocketbook. It is extremely selective — easy to adjust — tunes sharply, receiving all broadcasting wave lengths up to 600 meters. Works equally as well with dry cell tubes as with standard six volt tubes. Its light weight (weighs only 6 pounds) makes it ideal for touring, camping, etc. The cabinet is mahogany finish, made in Grand Rapids, the world's greatest furniture center. 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