dave.harper wrote:
-ex- wrote:



From what I've read here and elsewhere, I'm debating either making a
spider coil or a tight wound 4" cylinder ( about 1" length). Is there
any significant advantage to either?

They're going to be very similar in performance. If you do the solenoid
(cylinder), go with one wire spacing between turns instead of tight
wound. Thats been pretty well proven to give a bit better Q. And 16-18
ga wire is also in the 'best' range for both the spider-web and
solenoid. Next step up would be some serious litz wire.


I can see with a powered ferrite core how the spacing would make less
of a difference... but if tight winding results in a lower Q/other
effects, why space the windings for air-core, crystal radio coils,
period?

I'm not 100% sure I understand the question....On a
rook/basketweave/spider coil there's inherent spacing already. And a
solenoid coil will also do better that way...on larger coils. The way I
understand it is that there are several factors at work - primarily
interwinding capacitance and overall l/d ratio. In practice, as you
change one you also change the other. You can compensate one for the
other somewhat with a different diameter coil, different gauge wire, etc
but the general concensus is that 4"/16-18 wire/~1 wire diameter spacing
is pretty close to the best you can squeeze out of that class of coil.

HTH.

-Bill