Short Wave Radio Demonstrator
Thes items were purchased around 1940 and demonstrate a number of  electromagnetic phenomena - standing waves on a wire, measurement of frequency, high frequency oscillations, transmission of radio waves, polarization, composition of two plane polarized waves, coupling, measurement of electromagnetic field intensity, transmission of polarized waves through a screen, standing waves in space, and standing waves on a solenoid. The wooden box was most likely built here at UVM. The instructions that came with the apparatus can be viewed here.   The 1929 Cenco catalog descritpion is posted here.
The apparatus in the picture to the left is set up to demonstrate electromagnetic standing waves.  The oscillator is set up with the solenoid, which has about 12 turns/cm.  The nodes and antinodes are detected with the neon wand to the left in the picture.  For a movie of this effect, click here.   The oscillator frequency was measured at 94 MHz, and the resulting wavelength of the standing wave pattern was observed to be 21 cm - seemingly off by a factor of 2. This result can be explained by treating the solenoid as an anisotraopic helical resonator, for a slightly more detailed explanation go here. More information can be found at and
The two receiving antennas with detector bulbs are to the left, the oscillator is fitted with both horizontal and verticle antennas.
Here the two capacitor plates are attached to the oscillator, which drops the frequency to around 29MHz.
The neon wand at a node.
The neon wand at an antinode.

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