Here is the photo link published yesterday:
"Did you look at the pictures? http://www.qsl.net/kd1jv/cone.HTM"; That is
the start of one, with one parallel line element wound, and holes drilled
for a second. Thanks again to Steve Weber for this shot.
Note: In USE, You MUST turn the antenna so that the narrow cone end is
against the ground, with ground screen under it, or 30 radials, or it will
not work as efficiently. ( Steve's picture was taken with the antenna
supported so that we could see the construction of how to wind the elements
and for his first test before he knew to have the wide cone end pointed up.)
This is a vertically polarized antenna, I think a misstatement that it was
horizontally polarized might have crept into an early post in my excitement
and late night hours. :-)
Today we tested a 10m model that is a more narrow cone, but still made of
no. 10 wire paired with no. 12. This one has only two parallel line
elements. However, it has greater than 60 per cent efficiency with the
Wheeler Cap test chamber.
We are still tweaking its length and height, so I will publish those when it
is set as a tuned model.
We determined that raising the antenna above the ground, and ground plane,
moves it significantly away from resonance.
You would have to mount it on a solid cylinder of aluminum if you raise it
above the ground plane. We had it working in air at 27 MHz. We put it in
the buoy chamber, a plastic pipe affair. It moved it down to 25 MHz.
Trimming over a foot moved it to a point where we wished to test today in
10m band. But, it never regained zero reactance on the Smith Chart. You
trim from the shorted end of each two wire element, then reshort the wires.
It is really fun watching Smith Charts being plotted in real time. We had
100 ohms impedance and 2:1 SWR, and about 150 pf capacitive reactance at
best with the antenna raised some three feet or so above ground. Lowering
(inductance) of the connections to ground plane helped, but the best thing
is to have the antenna at the ground plane. This could be with tuned
radials; we did a demo with Ham stick radials to prove that. We think tuned
shorter radials would work as well, and that is the direction we take next
in tests.
What this means it works BEST at ground level on a ground screen, or on a
patio/ balcony floor with 6 foot square screen under it, with feedline going
thru the middle of the ground plane, NOT on top of it. Bring the feedline
off under the plane, by putting low feet on the plane. We are feeding the
prototypes with RG 58 coax. If ground mounted, move conductors away as you
should for any vertical antenna. If on a roof, you mount it with cone wide
end up, on a 6 foot square ground screen. We started with copper screen,
but aluminum will work if you get solid low inductance connections to it.
This might be a bolted connection with metal washers for improved lowered
resistance.
Thanks for the continued interest,
Stuart K5KVH
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