The loss is the same (probably), but the current profile at the antenna
is different (definitely).
Dave AB7E
On 7/3/2025 4:10 PM, Wes 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@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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