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
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