Topband: Inverted J antennas?

[Dave Cuthbert]

Rudy, N6LF, wrote a great article on his elevated radial experiments.

https://www.antennasbyn6lf.com/2012/02/elevated-radial-ground-systems-some-cautions.html

Rudy says,
"1) Use at least 10 to 12 radials.
2) Make an effort to have the radial system as symmetric as possible.
3) Keep the radial system as far as possible from other conductive objects.
4) While it is certainly possible to use almost any height for the
vertical, I suggest you start with H = λ0 /4 and trim the radials for
resonance. This makes H a little tall, but it shortens your radials
(especially if you’re using 10 to 12) and raises the feed point impedance a
bit.
5) Use a balun or common mode choke on the feed line at the base of the
vertical. To be effective, the balun should have a shunt impedance of >2
kΩ. 6) If you have a special problem situation by all means model some
trial solutions first. That will save you a lot of time over cutand-try in
the field. If you can't afford NEC4 software, the free NEC2 software will
still be very helpful. (

On Tue, Jan 12, 2021 at 8:48 AM <sawyered at earthlink.net> wrote:

> Mike,  All ¼ wave verticals have the same elevation angles.  The question
> is
> what is the feedpoint efficiency which is dominated by the ground.  That
> ground is a combination of your soil characteristics and the radial field
> design.  In my opinion, 2 elevated radials about 5 ft above the ground is a
> poor ground system for good performance.  Elevated 160M radials really need
> to be more like 20 – 25 ft above the ground to be efficient.  Otherwise, my
> experience has been you are way better off putting a lot of them on the
> ground vs a few in the air – below 10 ft.
>
>
>
> One thing to try is take a Z + R reading at the actual feedpoint as it is
> now and add 2 more radials.  If the R drops by more than 0.5 Ohm, then keep
> adding.
>
>
>
> I started with an R of about 24 Ohms with 4 radials on the ground and got
> it
> down to 12 Ohms by adding radials.  I have 44.  I could not see any
> difference with the last 4 so I stopped.  I have 2 T top verticals in phase
> and they are 260 ft apart.  And the same result occurred on both.  That is
> highly a function of my rocky (Granite) soil here.
>
>
>
> 73
>
>
>
> Ed  N1UR
>
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