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From: "Steve Thompson" <steve@eltac.co.uk>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 20 Nov 2002 09:40:00 +0000
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Subject: Re: LF: When you fix one thing...
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On Tuesday 19 November 2002 22:05, G4WGT wrote:

> I have made some progress on Spiral Top Load antenna, 310 cms corner to
> corner, 16 turns at 8 cms spacing (didn't want to go too tight). This
> produced 0.432 mH with (81 mtrs of wire) single spiral  & 1.424 mH with
> (162 mtrs of wire) double spiral, that's as far as I have got, transmitter
> almost finished, will keep you posted.
Please can someone confirm if I'm getting my analysis of the spiral (or other 
top) loading right?

Consider 30m toploading wire, about 150pF (-j7800). Putting 1.4mH (j1200) at 
the top of the vertical gives a net -j6600, or 177pF - equivalent to 35m of 
top loading without any inductance.

With 60m toploading, 1.4mH increases the effective length to 86m - starting 
to get worthwhile.

Thanks,

Steve