At 15, AM 2007-10-19, Rick K6VVA wrote:
>My understanding is that use of the 160m loading coil for the HF-6V limits
>the power to 500w on 160m.
>Q: What if the 160m coil is left off, and 4 sloping top hat wires were
>attached to the top of the vertical? Any idea what the length(s) would have
>to be, or would this even work? Is it true that top loading narrows the
I haven't seen any more follow-up regarding optimization of this
configuration, but I'll throw in the results of my modeling in EZNEC
(NEC-2 engine). I used the parameters discussed, and varied the
length of the four sloping (at -30 degrees from horizontal) top
loading wires from 10 to 65 feet long in 5 foot steps, plus just
under 66 feet where the system is resonant without a loading coil
(and the ends almost touch the ground). I ran with a top load at 90%
and a base load for ground system losses of approximately 2 and 10 ohms.
I'll send a copy of the Excel spreadsheet (which includes charts of
gain, bandwidth, loading inductance, and feed R) to Rick and the gang
who posted comments, but to summarize, the best gain (-1.17 dBi) is
for a top load with wires 30-35 feet long for 2 ohm ground. For 10
ohm ground and top load, 15 foot wires give best gain (-4.42 dBi),
although the loading inductor may be impractical. For base loading,
the gain is -1.44 dBi with 35-40 foot wires and 2 ohm ground. For
base loading and 10 ohm ground, peak gain is -5.49 dBi with 25 foot wires.
The self resonant (no loading inductor) configuration has poor gain,
but lots of bandwidth, but a more realistic configuration with the
ends of the top load wires somewhat higher than the 1 foot (which
results from a 30 degree slope) might do OK.
I also looked at the effect of varying the number of top hat wires
from 2 to 8. Using 3 or 4 wires definitely pays off (at least 1 dB
better than 2 sloping wires), but going from 4 to 8 wires makes only
a small difference in gain (0.3 to 0.5 dB) and a negligible increase
For comparison, I ran numbers with 25 foot non-sloping top hat wires
(good for about 1 dB) and a full size 1/4 wl vertical (about 2 dB
better than the best sloping top hat version over 2 ohm ground and
about 4.5 dB better over 10 ohm ground).
To state the obvious, an EXCELLENT ground system with lots of copper
on the ground is a must with these short antennas. It is also
necessary to make sure the loading coil doesn't arc or melt at the
1500 watt power level.
If anyone else wants the spreadsheet or modeling details, reply off list.
73, Terry N6RY
PS - I have a 26 foot version of this antenna, and I think I'll
shorten my 50 foot top hat wires a bit and increase my loading coil
to pick up a little gain. Where they fit, a few full-size 1/4 wl
radials will be added as well.
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