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 The Xtal Set
Society Newsletter |
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| Volume 8, No. 3 | May 1, 1998 |
IN THIS ISSUE (#42) MAY 1, 1998
Variocoupler and Variometer Primer |
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| The variocoupler and variometer are similar in that they both
have a coil that is variable to another coil. These two coils are called the
"Rotor" and the "Stator". The Rotor is the variable, or rotating coil.
The stator is the stationary coil that the Rotor turns inside of. Included with this
discussion are circuit and pictorial diagrams for building your own variocoupler and
variometer out of common salt boxes.
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| Figure 1: Variocoupler Details The main difference between the variocoupler and the variometer is that the variocoupler's rotor and stator are independent of each other. See Figures #1, #3, & #4. The two windings are inductively coupled to each other. This inductance decreases, as the rotor is rotated out-of-phase to the stator. In other words, when the two coils are in a position where the windings are in the same direction, they are in maximum phase to each other and the inductance between the two is at maximum. By the same token, if the rotor is turned 180 degrees, and the two windings are in completely opposite directions to each other (totally out-of-phase), then the inductance is at a minimum.
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| Figure 2: Variometer Details The variometer's stator and rotor are different, in that they are connected in series. See Figures #2, #3, and #5. To make Figure #5 complete: connect "A" to "G" and "B" to "H". I left these disconnected on the diagram as you may want to experiment, by hooking up different configurations than the conventional one explained above. The change that occurs when the variometer is turned from "0" to 180 degrees is only a few microhenries, so a load on the coil and taps are used to give a wider range of variance. You could use a variable capacitor across the stator, but that would be no fun. To make your variocoupler and variometer see Figures #1, #2, #3, #4, and #5. (If you are not familiar with winding coils or other basics of crystal set design and building, get the book Radios That Work for Free. I think this is one of the best books for beginners on the market.) Leave the beginning and ending of the windings about 6 inches long. Leave the wires from L-3 (rotors) about 9 or 10". Make certain that L-3 can freely rotate 180 degrees without the wires binding. Run the wires....
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