[Elecraft] Small QRP antenna

[Edward R Cole]

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
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