The Wrangell sentinel., 1923-04-12
RADIO
INTERFERENCE OF
 RECEIVING SETS
Each, When Tuning for Distant Station, Acts as a Continuous
 Wave Transmitter.


 tons, was due to a combination or the carrier waves of two stations which were very nearly on the same wave length. There is another series of whistles always present which very much resemble the whine of mos quito both in tone and amount of an- noyance produced. These are caused by the receiving sets of other listen CTS Every receiver using a vacuum tube detector with regeneratiye cir cult is a potential transmitter. In fact 1t contains all the essentials of & radiophone transmitter on a small scale
 The detector tube when oscillating produces oscillation exactly similar to the carrier wave of the radiophone stations. The frequency. or wave length of this wave can be varied by changing the tuning of the receiving tuner.
 The usual procedure in tuning for a distant phone station is as follows: Put the detector tube in an oscillating condition after the tuner has been ad- tusted near the point where experi- ence has taught us to look for the broadcasting stations, then move the dial slowly across the approximate point where the stations are usually heard. The carrier waves are located by a whistle which starts at the upper limit of audibility and goes down the scale until it becomes so low that it is no longer a note. At this point the set is in exact resonance, and if the ticker. coupling. or plate tuning in, ductance is decreased until the detec- tor tube stops oscillating. the very best adjustment is obtained for recep- ton of that particular station.
 Unfortunately while this listener is going through this operation his re- ceiving set is acting as a continuous wave transmitter, and is producing some inharmonious walls in the phones of his neighbors who happen to be already on the wave of the same station. The continuous wave sent out by the receiver combines with the wave ol tllC idhSihittlhS tion, producing an audible note. If the operator could tune his set as sim ply as was described above there would be very little interference. but he usually whistles back and forth across the wave of the transmitting station several times. Often several listeners who have been getting the concert perfectly will get restless be- tween selections and get their tubes to oscillating and whistle up and down a few times.
 All listeners should be very careful lating condition as much as possible to reduce this annoyance of interfer- ence between receivers.
 Opinions seem to vary considerably in regard to the comparative amounts of energy inducted into the antenna by the single circuit" or conductively coupled. and the three circuit" or inductively coupled receiving set
 Previous to the introduction of the single circuit very little trouble had OCCA CApCiiCu1CN VIII pCdt uolCS from receiving stations. This was no doubt due to the fact that receiving sets were rather few and far between; also up until a few years ago there was very small percentage of C. ". telegraph and phone stations so that there was no reason why an amateur should keep his tube in oscillation condition. On the contrary, he was very careful to keep 1t just below the oscillating point, that being the most sensitive adjustment for spark signals
 With the telephone and c. W. tele- graph transmitting stations, 1. e., tube transmitters, came the single circuit tuner with its extreme simplicity of adjustment, which was so well adapt ed to the very sharp tuning of the new transmitters. And with the ad- vent of these new transmitters came the necessity for making the detector tube oscillate in order to locate a sta tion on the scale of a receiving tuner. Naturally then the interference be- tween receiving sets became notice able at about the time that the single circuit sets became numerous, and this helped to prejudice the minds of the radio public against this type of re- ceiver However, the fact that the single circuit arrived at about the game time with the interference was by no means the only reason for believing this tuner to be the main cause of the trouble.
 For instance in constructing single circuit or conductively coupled tuner the difficulty is in obtaining regenera- tion at all points on the scale. This seems to show that there is more re- sistance in this circuit than in the in- ductively coupled type. The main point of difference is the close coupling to the antenna Being con- ductively coupled, the coupling to the antenna circuit Is at maximum at all times. This causes the ra- diation resistance to be high. which apoms to ho the factor that ~keeps