On Thu, 02 Apr 2009 09:37:06 -0400, Bob Dixon wrote:

I was referring to the tuned twinlead system shown in figure 6 of the
original reference http://www.bencher.com/pdfs/00361ZZV.pdf
How are the lengths determined (obviously not a quarter wavelength)?

Hi Bob,

Obviously not? Of course it is for at least 40M (overall length); and
of course it is for at least 10M (to the first notch); and half a wave
for 15M and half a wave 20M. Half waves are two quarters....

Those dimensions are the intent of tuned radials. Tuned radials have
some integer relationship to a quarter wave. Some commercial designs
might offer radial reactance (non-quarterwave relationship) to balance
out the inverse reactance seen in the vertical, but I don't think we
see it here.

Proximity to earth will change all of this, however. Layout a longer,
overall length without cutting the notches and tune for the lowest
band. Use that last 3 foot section to do this (like making it 6 feet
long at first). I would then work on the first notch for 20M and cut
it out long too (the 3'10" section is redundant and thus expendable)
so you can shorten towards the base. Then I would work on the second
notch, but cut closer to the base (say, at 18' from the base) and trim
towards the end to tune in 15M.

The same thing (compactness) could have as easily be arrived at by
using in dependant wires, all cut to quarter/halfwave and bundled
together. There is nothing particularly remarkable about the twinlead
in its own right except for mechanical stability.

73's
Richard Clark, KB7QHC