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Re: Flat coils & undamped waves (was Wire Length)

Original poster: Mike <megavolts61@xxxxxxxxx>

There may be one advantage in using flat spiral coils - they may have more self capacitance and hence allow a lower resonant frequency. But aside from that, I can't see any serious advantage

    Answer to your question is that "inductors are inductors" no
matter what the shape and flat spirals have no special and desireable
electrical properties.  They appear in may of the Tesla photographs,
probably because they were more photogenic than cylinderical coils of
wire.  Some of the patent drawings appear to show spiral coils but I
suspect that was draftsman's license.  I don't think there are any
flat spirals shown in actual use in CSN, although there is at least
one picture of same..  Flat spirals were used in some transmitters in
the "early days of wireless", primarily for mechanical
reasons.  Examples - they were convenient to mount on large flat
panels.  Some were mounted "swinging gate fashion" where it was
desired to adjust the degree of coupling between two different
coils.  By the time that vacuum tube transmitters came into general
use (circa 1917-1918) solenoidal coils came to be used
universally.  In general they have higher Q for the same amount of
copper and that was more important for CW than for damped waves where
the circuit Q's tended to be much lower.


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