You would think this simple antenna should give one no problems.
Maybe some expert here can help solve this problem.
Unfortunately I can mount it only up 22' on a chimney mount. Currently
fed with 61' RG8X and a 6 turn 6" diameter RG213 choke at where the
feedpoint spreads in Y fashion to the element halves.
It works with one problem. The 15M SWR is 2.7 at the low end of the CW
band. The settings were made for CW. The resonant point in the HyGain
manual for this "CW" setting is 21.175 MHz. That's what I see. The
curve has not got the Hygain bandwidth. The lower frequency slope is
quite a a bit larger. The above resonance slope doesn't depart too much
from HyGain's. This larger slope is what is causing the high SWR at the
low end of the CW band.
I'm using the K3 SWR readings. They are not that different from what an
AUTEK RF-1 gives.
The elements are like this:
--------Y-----T10---X---T15-----Z---- Half driven element.
Where X,Y,Z are dimensions.
T10 is the 10M trap
T15 is the 15M trap.
I wanted to try and move the resonance on 15M down the band about 85 KHz
to bring the CW SWR under 2:1. I determined that that meant lengthening
X by 3/8" on the driven element half and 0.5" on the reflector half
element. This was determined by extrapolation of the slopes of the
length curves given in the manual.
"This height at 15M is 1/2 wavelength so it should be high enough to
avoid too close to ground effects. Obviously it is about 6' over
standard shingled roof.
It was expected that the bandwidth is less than the HyGain manual gives
for 70' up."
I made these length changes and NOTHING changed. The resonant point was
I've ruled out backwards 10M traps and driven element 15M traps are
indeed on the DE. 20/10M are fine. Turning the beam 90 degrees doesn't
So what magic dimension does one change to bring the resonant frequency
down on 15M?
And why 15M and not the other two bands.
"USE A TUNER" is not a solution.
(Previously had a TH-2 at 80' on a HAZER arrangement. Tweaking it was
straightforward by numerous up/downs to 40')
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