Hi Ford,
You found a good use for cattle panels. I hope they don't start
turning up missing around here, if local hams start installing
verticals!
> I placed a 54" square piece right over the post used to support the weight
> of the vertical. 1 - 16' panel was then placed at each edge and welded
> together to form an "X" shape around the tower. An 8' copper clad ground
> rod was placed right at the base of the vertical and welded to the panels.
> Flat washers were welded to the panels too. These act as ground
> connections for the vertical -- both the 80 main vertical and the 40 meter
> sleeves. After a few weeks of laying on the grass, I can't even see the
> panels any more (two mowings).
It sounds like your ground screen is what, 24 feet in radius? And
the average radius is less than that a bit? You have the equal of a
bunch of 24 foot radials. 24 feet is about 1/10th of a wavelength. (If
that is the right radius). With 1/10th wl radials, a couple dozen and
a couple million have about the same impedance, and certainly will
not be an ideal ground system by any means..unless you live in a
salt marsh.
> I am getting a feed point impedance of 45 +j5 at 3.5 mhz. 44 +/-j0 at
> resonance.
> My question is this: Mininec 3 predicts (perfect ground for impedance
> measurements) a feed point impedance of 36 +/- j 0 at resonance. Am I to
> assume then that there is about 8-9 ohms of ground loss? If so, is this
> good, average, or poor for a full sized vertical?
Probably average for an amateur station, and poor for a commercial
installation. That resistance will NOT reflect all of the ground
loss....only the loss associated with feeding the system.
You will have loss just outside the ground screen that is caused by
induced currents that does not really show up in the base
impedance.
73, Tom W8JI
W8JI@contesting.com
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