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R. F. Amplification Without Distortion
or Reradiation
By EDWARD LINDLEY BOWLES
Instructor in Electrical Communication. Massachusetts Institute of TechnologyMany beginners have been intrigued by the claims made for various involved circuits. For the novice, radio frequency is complicated, and its use does not always result in greater range with a homemade outfit.
You will do well to attempt R. F. amplification only after you have mastered a regenerative receiver and A. F. amplifier. This is especially true since the change in the broadcasting wavelengths has been in effect, because few transformers will cover satisfactorily a range from 220 to 550 meters.
We do not wish to discourage the use of radio frequency, but we do wish • to discourage indiscriminate buying which results in disappointment to the buyer and ultimate reduction of sales for the dealer. — The Editor.
TO-DAY the question of radio-frequency amplification is uppermost in the minds of both the amateur and the broadcast listener. Since the new allocation of wavelengths, the broadcast receiving set is not confined in its operation to wavelengths in the neighborhood of 360 and 400 meters, but it must range from as high as 550 meters to as low as 220 meters.
Volumes have been written on radiofrequency amplification, in which proponents of particular methods have been eager to convince readers of the merits of their choice circuits. Yet, many of those who have attempted to construct their own radio-frequency amplifiers for short wavelength work have been disappointed in the results. This is due to an in
FIG.
R. F. amplifier showing a tuned primary transformer
adequate knowledge of the functioning of the units employed, and the natural tendency to judge as "best" the circuits bearing high-sounding names and blessed with good press agents.
Many so-called radio-frequency amplifying transformers, or amplifying devices, which have been advertised for the shorter wavelengths, have proved to be poor. In fact, the writer has found that in some cases so-called short wavelength radio-frequency amplifying devices have done more harm than good. It seems only fitting that since radio broadcasting has reached a point where many wavelengths must be used in order to relieve congestion, and since these wavelengths must be "short, " the broadcast public should have a general idea, at least, as to why there is likely to be difficulty in applying only general ideas of radio-frequency amplification to circuits which they have already constructed or which they propose to construct, in order that these difficulties may be avoided.
Technical analysis has shown that R. F. amplification is more effective than A. F. in bringing in distant signals. Of course, if a signal is too weak, no matter how good the receiving set may be, the signal will not come in. In other words, there must be a slight disturbance, at least, in the neighborhood of the antenna or loop, in order that the re