I very vaguely remember there was a different optimum length for the
others, thanks!
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 7/18/2020 12:25 PM, W2xj wrote:
That only applies to class A stations with protected skywave. Otherwise,
something near 225 degrees is best.
Sent from my iPhone
On Jul 18, 2020, at 11:33, Fred Jensen <k6...@foothill.net> wrote:
And the Texas Bug Catcher, Webster BandSpanner, SteppIR's, et al. All
represent changes to the antenna itself, which would also include changing the
height [e.g. cranking the tower up and down] and possibly cutting down nearby
trees or metal buildings [:=). Any change to the antenna itself or its
near-field environment will affect the feed point complex impedance. This
would include adding traps, inductors, and capacitors to the antenna.
When you're done flutzing with the antenna itself, you are stuck with whatever
complex impedance you find at the feed point. AM broadcast verticals are
generally engineered for coverage near the edges of the market area, meeting
non-interference FS requirements, and minimizing self-cancellation between the
ground and sky wave. Something in the vicinity of 195 degrees is generally
optimal. They are not usually resonant and there will be fixed matching
network(s) at the base(s) ... AM broadcast stations aren't known to QSY much.
I'm not familiar with the TurboTuner however many mechanical antenna adjusters
operated by driving the phase angle between voltage and current to zero, that
is effectively bringing the antenna into resonance so the feedline sees a
resistive load. It's up to you to design the antenna so that resistive load
matches the characteristic impedance of the feedline OR put a matching network
between the feedline and the antenna feedpoint OR tolerate the SWR on the line
and put the matching network in the shack. Pick one.
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