Thanks to personal replies from several of you, a satisfactory solution
has been found.
Adjusting the Y dimension outward 1" was the answer. It moved the 10M
band SWR curve to a resonance at 28.000 but it still gives me up to
28.5MHz at 2:1.
The 20M band will never be all modes at this height. Enough coverage
for CW and high RTTY is now present.
The real solution is to get it up at 50'......
73 de Brian/K3KO
On 8/26/2012 20:53, Brian Alsop wrote:
> 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')
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2178 / Virus Database: 2437/5225 - Release Date: 08/26/12
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2178 / Virus Database: 2437/5225 - Release Date: 08/26/12
>
>
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2178 / Virus Database: 2437/5227 - Release Date: 08/27/12
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|