>The results:
>
>Open unused turns: F=4.8236 MHz, Q = 122
>Shorted turns: F=5.2293 MHz, Q = 99
>
>Not only did the Q decrease by about 20% but the effective
>inductance also decresed by about 20%. Unfortunately I do not
>have an coil of 5 micro Henries and the same construction to test
>the Q with no unused turns.
Everything has a trade-off. The trade-off with not shorting unused turns
on a tapped coil is the chance of producing eyebrow-raising RF voltages
across the unused turns. I was sketical until I saw the result. Now I
always short unused turns. Some builders aptly call it the Tesla Coil
effect.
OTOH, if separate coils, oriented alternately at right angles. are used
in lieu of a tapped coil, the losses you observed are obviated. The
trade-off is that doing so takes more chassis space than a tapped coil.
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|