Jim, K7JEB wrote:
Jouko, OH5RM wrote:

Take 20m of wire, that is half of a dipole.
Put a 1/4 electric wavelength shorted stub for 10,1MHz so that the open end
is 7,25m from center and the shorted end pointing to the tip of antenna. One
side of stub is the 20m wire itself, like in the upper picture.

I did just that with EZNEC, but with a free-space dipole. Without the
stubs, the antenna resonated at 3.6 MHz. With the stubs, that dropped
to 2.75 MHz and additional low-impedance points were noted at 6.5 and
11 MHz. The patterns at 2.75 and 6.5 had the desired dipole shape,
but the 11 MHz pattern had multiple lobes.

Great minds think alike. :-) I was doing the same thing
at different frequencies. I noticed that a 1/2WL dipole
with 1/4WL stubs on each end tends to resonate on frequencies
in a ratio of about 2.57:1. 18.14/2.57=7.06 so such an
antenna should be resonant on both 17m and 40m. EZNEC
agrees. Here are the approximate dimensions for the dualband
40m/17m antenna. Cutting and trying will be necessary for
fine tuning to resonance. Note that the antenna is about 13
feet shorter than a 1/2WL dipole on 40m. It has a dipole
pattern on both 40m and 17m and a 50 ohm SWR less than 2:1
on both bands. It appears to be linear-loaded on 40m and
stub-matched on 17m.

26.8' 26.8'
+-------------------------FP-------------------------+
| |
+------------ ------------+
13.3' 13.3'

Since 10.125/2.57=3.9 MHz, this antenna should be scalable
to become a dualbander on 75m and 30m.
--
73, Cecil http://www.w5dxp.com