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CONSTRUCTION AND USES OF A LOOP RADIOPHONE TRANSMITTER
By ZEH BOUCK
THOUGH numerous articles have appeared extolling the advantages of the loop radiophone transmitter, to the knowledge of the present writer, no practical description of their construction and operation has been published. In discoursing on the subject many authors have emphasized (and not unduly) the directional effect of this type of transmitter and the resulting communicative possibilities due to the lessened QRM (interference). However, the radiation limitations necessarily
be easily transformed into a loop transmitter in either of two ways. The simplest, though probably less efficient method, is to substitute the loop in series with a variable capacity, for the ordinary aerial. In the second system the loop is used directly in place of the conventional inductance and where necessary, to sustain oscillations, a condenser (variable preferred) replaces the capacity afforded by the open antenna.
A glance at figure one will reveal that I have employed the second method wherein
AMPLIFIER
imposed upon the loop by its electrical characteristics, make distances comparative with those secured with conventional antennas an impossibility except by a lavish expenditure of time and money upon ultra apparatus. For this reason, though I shall describe a transmitting loop capable of reliable communication over short distances, 1 shall rather emphasize the other adaptations of the loop as they appear under the general classifications of Novel Uses (magical illusions, etc.) and Laboratory Experiments.
For all three purposes the constructional details are identical, with the exception of the intercommunicative set, in which a slight elaboration of the basic type permits receiving and transmission with the same loop, tube, and tuning apparatus.
Before describing the set made and successfully experimented with by the author, it is well to mention that any wireless telephone at present radiating from an open antenna, can
the "Split filament circuit" has been superTicially altered by the substitution of the loop X for inductance L and condenser C i for the antenna and ground.
The loop was constructed on a twenty-inch square frame, and wound with seven turns of number twelve bare copper wire spaced three eights of an inch. The variable condenser Ci is of .001 maximum capacity, and the fixed permittance C2 (a bypass condenser) is the size generally shunted across spark coil vibrators. However, if such is unobtainable, or the experimenter contemplates employing a plate potential in excess of two hundred volts, he is advised to build up a condenser of thirty plates of 2" by 2" tinfoil separated by mica sheets.
The high voltage, B, may be a convenient source of D. C. over one hundred volts which in the case of portable sets will probably be found in block B batteries or a small dynamotor operative from a six volt supply.
Almost any amplifier tube of sufficient hard