There is described a new type of vacuum tube voltmeter which makes use of the heterodyne principle. The use of this meter is restricted to the measurements of steady, single frequency voltages in the audio and lower radio frequency range.
The meter has a linear characteristic and is extremely sensitive, the model described having a sensitivity of four scale divisions per millivolt. A sensitivity three times as large as this has been obtained by employing a different type of galvanometer and it is probable that by using the best type of galvanometer available this could be increased to the order of one division per microvolt.
Measurements may be made of weak signals which are accompanied by a relatively strong noise background.
It is shown that when the proper values are chosen the calibration is little affected by small variations in the voltages of the various batteries which are used. An exception is the filament voltage of the rectifier tube which must be held constant.
© 1928 Optical Society of AmericaFull Article | PDF Article
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