Sounds like one or more of the 15m traps is defective. Insects, etc.,
can cause those problems.
73
Don
N8DE
Quoting Brian Alsop <alsopb@nc.rr.com>:
> You would think this simple antenna should give one no problems.
>
> Wrong.
>
> 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
> identical!
>
> 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
> change anything.
>
> 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.
>
> Brian/K3KO
>
> (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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