On Feb 23, 3:11 am, Ian White GM3SEK wrote:


I'm not so sure. A 24ft vertical is about 0.18 wavelengths at 7MHz, and
about 0.09wl at 3.5MHz. It will require a large series inductance to
resonate it at 3.5MHz, and will also require some series inductance for
7MHz.

That inductance must be provided by either an external loading coil or
by the auto-tuner. The question is: which will have the smaller loss, a
large and well designed external coil, or the tiddly little toroids
inside an auto-tuner?

I was kind of thinking the same way.. In general, I would usually
prefer
the larger coil, even with it's problems.
I think a larger part is the top loading, if used.. If no top loading
were used
for the 24 ft whip, I could see it being a toss if the loading coil in
the tuner
was small and rinky dink. It could easily lose to the center fed if
the tuner
is poor.
But then you also should consider current distribution through the
whip.
Can make quite a difference. If the 24 ft whip was fed with a tuner,
and
no hat was used, max current will be at the tuner coil.. Not really a
good thing.
But adding the hat will greatly improve current distribution through
the
whip, and pretty much cure that problem, assuming the hat is large
enough.
If no hat is used, I would always prefer a center loading coil. Mainly
for
current distribution reasons. But also cuz many tuners are overly
lossy
when used in such a manner. Note comparisons with a tuner fed whip on
a
car, vs a good center load antenna. In the average case, the tuner
fed
whip will be about 12 db down according to the mobile "shootouts".
As far as coil Q, 1000 is going to be pretty optimistic... 300 + -
would be
more easily obtainable.. And thats a pretty decent coil.
If ground radials are ignored, ground loss could easily swamp the coil
loss.
Of the two losses, I'd be more worried about ground, than coil loss.
But thats just my 29 cents worth...
MK