From Dave G3YMC
First apologies if one of my mails to Steve GW4ALG got posted on the reflector -
'pressed the wrong button' as they say!
Following this discussion, I suggest the following.
One standard bucket (UK size) can be wound with exactly 100m of 16/.2 pvc wire
gives an inductance of 3mH. I have two of these and arrange them concentrically.
Moving the buckets inside each other gives a reasonable control of the combined
inductance (I require 6.5mH to resonate my top loaded Butternut). One bucket is
tapped every 20 turns, for coarse adjustment of the inductance. A suitable
hold the inner bucket is made out of a compressed wad of paper, though the more
mechanically minded could design something less Heath Robinson! If I remember
correctly the dc resistance is a few ohms and quite acceptable for most powers
compared with earth losses.
This should work in most situations, however the earth losses of 400 ohms at
dampen the resonance such that the tuning is very broad.
I hope to get something about verticals on my website in due course, however I
most disappointed with its performance here - initial tests show my loop is
few dB better.
73s Dave G3YMC