Re: [TowerTalk] Good vacation antenna

[David Gilbert <ab7echo@gmail.com>]

Use the "Currents" data from EZNEC to plot the current profile of a base 
loaded vertical and compare that to the "Currents" profile of a 
non-loaded vertical of the same length.  Calculate the loss in the base 
loaded coil and subtract that from the drive level for the example 
without the base loaded coil.  If you can't understand the effect of the 
difference between the two current profiles I don't know what to say.
Or you can take the easy route and just don't believe me.  I really 
don't care.
Dave   AB7E


On 7/3/2025 6:27 PM, john@kk9a.com wrote:
> You're not alone Wes.  I also do not understand how having an inductor at
> the tuner for an electrically short antenna has a different effect from
> putting the inductor at the antenna base.
>
> John KK9A
>
>
> Wes n7ws wrote:
>
> I'll confess some difficulty (probably my failing) in understanding your
> point(s).  To try and simplify the situation to something my pea brain may
> understand, let's use a toroid at either location.  Now tell me what the
> difference is.
>
> Wes  N7WS
>
>
>
> On 7/3/2025 3:39 PM, David Gilbert wrote:
> > Because whatever current is left after the loss in the tuner still makes
> it to
> > the antenna but doesn't have a major portion of it compressed inside the
> coil
> > where it matches and also suffers loss but doesn't radiate.  Radiated RF
> is a
> > function of BOTH current and length.  If it was otherwise we'd all be
> using
> > parallel tuned circuits with large coils on 40m instead of aluminum tubes
> and
> > wires.
> >
> > Dave   AB7E
> >
> >
> >
> >
> >
> > On 7/3/2025 2:11 PM, Wes Stewart via TowerTalk wrote:
> > >     So you move the loading coil from the base of the antenna to inside
> the
> > > tuner in the radio (with some coax in between).  How does that affect the
> > > radiation efficiency/?
> > > On Thursday, July 3, 2025 at 01:57:33 PM MST, Jim Brown
> > > <jim at audiosystemsgroup.com> wrote:
> > > > https://www.dxengineering.com/parts/cha-ss25
> > > That looks like a great solution, Dave! I strongly suggest against a
> > > loading coil for 40M, using a tuner built into the radio instead, with
> > > or without some top loading. Loss in short lengths of decent-size coax
> > > on 40M is pretty low, even with significant mismatch. An excellent study
> > > in QEX about ten years ago showed that inductive loading at the base
> > > greatly reduces the radiation efficiency, because it's at the current
> > > maxima! The study included the construction of multiple configurations
> > > of loading, and very rigorous measurements.
> > >
> > > 73, Jim K9YC
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