Signedetched and white filled on front panel: STANDARD FREQUENCY / MEGNETOSTRICTION OSCILLATOR / CRUFT LABORATORY / TYPE AN No. 1
on face of right hand meter: PAT. NOV. 6, '88 APR. 29, '90 FEB. 17, '91 OCT. 4, '98 JULY 16, '01 / MILLIAMPERES D.C. / WESTERN ELECTRICAL INSTRUMENT CORP., NEWARK, N.J., U.S.A. / MODEL 301 No. 885288
on face of left hand meter: PAT. 1,579,849 1,597,256 / VOLTS A.C. / WESTERN ELECTRICAL INSTRUMENT CORP., NEWARK, N.J., U.S.A. / MODEL 476 No. 27311
FunctionThis is a device that can produce a very stable frequency output, which can serve as the basis for a very accurate clock or as a standard for the frequency of radio emitters. It is a very innovative, unique design that uses the phenomenon of magnetostriction -the expansion and contraction of metals when magnetized- as the source of the oscillations.
The problem of accurate timekeeping and the production of stable radio frequencies was central to the development of radio, and when this oscillator was made there was only one other way of producing stable high frequencies, quartz oscillators (Also partly developed by G.W. Pierce), which were the subject of an intense patent dispute. This magnetostriction oscillator works on an altogether different principle:
It consists of a standard oscillating circuit (LC) composed of an inductor coil and a variable capacitor, connected to an amplifier whose output oscillates at the same frequency and feeds back into the oscillator. The key element of this system are two inductor coils (absent) that would be connected to the circuits, one before, and one after amplification. A long metal rod would pass through these. This rod changes its length in the presence of a magnetic field, and has a specific natural frequency of oscillation that depends on its material and geometry. Crucially, it also creates a magnetic field when expanding and contracting that can feed into the circuit. If one adjusts the radio oscillator's frequency to coincide with the rod's oscillation frequency, the output is very strong and stable.
In addition to radio uses, its output could be connected to a clock motor for very accurate timekeeping.
This is probably one of the earliest prototypes of this kind of device, built in the Cruft Labs by G.W. Pierce. For later, factory made versions, see RS1313 and the other oscillators linked to it.
Primary SourcesOther prototypes of this device are discussed in George W. Pierce, "Magnetostriction Oscillators," in Proceedings of the Institute of Radio Engineers Vol. 17, No.1 (January, 1929).
ProvenanceProbably from the Department of Physics, Cruft Laboratory, Harvard University.