I've stayed out of this discussion so far.
I can comment on building a J-pole for 10m and 6m. I used a 24-foot
tall 1-inch diameter aluminum mast held by a 8-foot section of
Rohn-25G "planted" in the ground (no concrete). I used 1/4 wave stub
space 2-inch running parallel to the mast from ground level on 10m.
the bottom ends were strapped together and coax was run up about
6-inches above the ground end with center tied to stub and shield to
mast. Good 50-ohm match over about 28.300-28.700 MHz and under 2:1
over a MHz bandwidth. I did not ground the J-pole other than that
provided by the short tower.
I added a 6m J-pole to the top section running a separate coax feed
and it had little effect on tuning the 10m antenna. I tuned it for
52-MHz FM but found the only repeater was at marginal distance with
no local activity so its not in current use (the 24-foot pole acts as
end support for my 80/40m inverted-V with long nylon cord so the two
antenna do not interact).
I did make a coax coil RF choke at base of the antenna to inhibit
common-mode radiation and coax was buried a couple inches deep for
about 50-feet run to the house. I always intended to add buried
radials but never got around to it.
I had this up as a web-page until my site was hacked a few years ago
and never restored it.
I also have a very-short inverted-L on 600m: 43-foot by 122-foot
which is currently down for repair. My radials were lain on ground
and at 70-foot not anywhere near 1/4 wave (465-foot). Ground
resistance is 20-ohms measured whereas radiation resistance is 0.83
ohm per EZNEC5. Obviously not efficient, but definitely QRP when
running 100w (less than a watt radiated). Worms are cozy! SWR
bandwidth is 5-KHz.
Of course neither are QRP portable antennas. One could make the 10m
version from ladder line plus 1/2 wave top wire either as a zepp or J-pole.
I think the zepp configuration would be nice for quick portable use
if you have two vertical supports (one could be an 8-foot aluminum
pole with standoff rod for the 1/4 wave section). I might give that
a look for use with my trailer in a campground while RVing.
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
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