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From: TTman on 19 Jun 2010 10:23
I have some data to make one to try out.... 6mm dia, 28 mm long but....
Does it matter what the spacing between the coils is, i.e. no of turns ?
Is the effective 'length' (pi x Dia x no of turns) = 1/4 wave ?
If I 'pot it' with hot melt glue, to make it 'rigid' will that screw it ?
Can I use any solid wire? 18swg TCW ? Or does it have to be enammel covered
?
TIA


From: Tim Wescott on 19 Jun 2010 23:09
On 06/19/2010 07:23 AM, TTman wrote:
> I have some data to make one to try out.... 6mm dia, 28 mm long but....
> Does it matter what the spacing between the coils is, i.e. no of turns ?

Yes. Like Mr. Hobbs said, it's a slow wave structure, and the coil
geometry (including turn spacing and wire diameter) affect the speed of
the wave along the coil.

> Is the effective 'length' (pi x Dia x no of turns) = 1/4 wave ?

Probably close, but it could be 1/2.

> If I 'pot it' with hot melt glue, to make it 'rigid' will that screw it ?

Almost certainly. I doubt that hot melt glue is a really high Q
dielectric, and it'll change your resonant frequency.

> Can I use any solid wire? 18swg TCW ? Or does it have to be enammel covered
> ?

Uninsulated is probably best. Your wire insulation is a dielectric, see
my answer to your hot glue question.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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