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Show (Edited by a. Doug-laa Wa,rdrop, Editor ol Radio MerchnaialnB.) I I -. . -j- sTei i i lPt''''Tl h wm; A High Signal Intensity Equal to Four Tubes Is Obtained From This Two-Tube Two-Tube Reflex Outfit. The principle of the reflex circuit depends de-pends on the ability of a three-electrode vacuum tube to permit currents of different frequencies to pass through It at the same time. The frequencies fre-quencies of the currents Induced in a radio antenna system are very rapid, varying In value from about 500 to 1,-000 1,-000 kilo-cycles per second, depending on wave lengths. This current in the antenna system Is generally termed the radio frequency current. In a reflex system these radio frequency currents are usually amplified to Increase their intensity before impressing them on the rectifier or detector, which converts con-verts these high frequency currents Into currents of audible frequency. After rectification these currents are then amplified as were the radio currents cur-rents by a three-electrode vacuum tube. Here lies the particular advantage advan-tage of the reflex system over other systems. In other systems, after rectification the rectified radio or audio currents are amplified by additional tubes for this purpose. In a reflex system before be-fore these input radio frequency currents cur-rents are rectified they are relm-pressed relm-pressed back on the tubes which amplified am-plified them at radio frequency, and when rectified are reamplified at audio frequency before being passed on to the receivers or loud speaker to be converted to sound waves. There are a number of methods of utilizing the reflex principle, among which are the type of reflex wherein the reflex action proceeds from the input in-put to the output tube in direct progression pro-gression and where the reflex action is performed in more than one tube. Then there is the so-called inverse duplex du-plex system wherein the reflex action Is not progressive, but Is inverted back toward the input tubes. In the Erla circuits the reflex action Is progressive from the Input, but is only utilized In one tube. Due to the complexity of controlling radio frequency it is not possible to successfully stabilize a system sys-tem wherein the reflex action is Included Includ-ed In more than one stage. It is not a matter of balancing the loads in the various tubes, as it can be readily shown that the loads caused by any audio signals on the tubes In these circuits are never such that the few micro-watts of radio signals addition, ally Impressed upon them would overload over-load them as has been many times stated. In general there are practically two forms of using vacuum tubes as radio frequency amplifiers, i. e. the coupling transformers may be either tunable or fixed. The tunable type transformers are so designed that they may be tuned, usually by a variable condense? In the other type 'the transformers cover a certain range without tuning. The latter are "broad" and make for unselective reception. It is imperative that if selectivity Is to be had where radio frequency amplification ampli-fication is employed the coupling transformers trans-formers must permit tuning adjustment by a variable tuning device such as a variable condenser. Because the transformer trans-former is actually tuned to the signal with this type of radio frequency amplification, am-plification, not only great selectivity Is obtained, but greater amplification Is likewise secured. , : Either a vacuum tube, two or three electrode, or any of the many forms of crystal rectifiers of high frequency currents can be used as a rectifier, we are told. However, in a reflex circuit, due to the particular location in the circuit and inherent characteristics of the detector, a crystal rectifier will be more satisfactory. By the use of the proper crystal rectifier an excellent controlling effect on the stability of the entire circuit may be had. This feature Is not generally known, but is demonstrated in the stability of the circuits using this form of a detector. Not every crystal rectifier which might possess high rectifying properties proper-ties will be found the best for this purpose, pur-pose, due to the fact that the crystal can be made to provide a stabilizing effect on the reflex action of the circuit. cir-cuit. The fixed type of crystal naturally natural-ly requiring no adjustment, if correctly correct-ly designed, affords the best form of rectifier for the reflex circuit. Another point of interest is the fact that not every audio transformer can be used in a reflex circuit. In a reflex circuit the audio transformer is associated asso-ciated with the radio frequency currents cur-rents of the circuits and requires a design de-sign and construction differing from the regular audio transformer. |