Quite a few years back I had a 40' Rohn tower with a system 36 by Wilson on it.
The tower was setup to tilt over on a hand winch with a ginpole. I could tilt
the tower over very near the ground with the system 36 tribander facing up into
the sky and tune it. The reflector was only about a foot off the ground. You
could predict the shift in the SWR curve when raised up after a couple of tries
and it worked very well. The system 36 needed to be adjusted for 10 meters and
I moved those traps in slightly to shift up the resonance on 10 and readjusted
the 15/20 section out slightly. Was really a nice little setup.Learned a lot
about tribanders there even though I didn't think the system 36 by Wilson was
very good. Unlike the Mosley System 36 it was copied off of.
But the point is you can adjust a yagi pointing it up in the air with the
reflector near the ground and predict which way and how much the SWR curve will
shift. Can't do this with a quad though is my experience.
Terry
KI7M
> On February 23, 2018 at 6:46 AM Charles Morrison wrote:
>
>
> Last year I prepared a Cushcraft 40-2CD and a HyGain 402BA for Field Day.
> Each would not show good sweep results and would not radiate well while
> the
> boom pointed up and even with the reflector end raised up three feet.
> 40M yagis just need to be up higher to test.
> -Charlie N1RR
>
>
> On Fri, Feb 23, 2018 at 9:26 AM, john@kk9a.com mailto:john@kk9a.com wrote:
>
> > > I have never tried tilting the a beam up. It seems like a lot of
> trouble,
> > especially with a long boom and I would not be confident that it is
> > still
> > tuned properly. It is quite easy to pull a beam up the side of a
> > tower
> > about a wavelength high and take measurements though 1/2 wl
> > multiples of
> > coax and then bring it back down to make any adjustments. I have
> > done this
> > completely by myself many times and my antennas have a nearly
> > perfect SWR
> > curve when mounted.
> >
> > John KK9A
> >
> >
> > From: "Ed Sawyer"
> > Date: Fri, 23 Feb 2018 05:57:39 -0500
> >
> > I don't find that the "point the beam skyward" method works that
> > well on
> > 40M
> > beams for doing the initial SWR test. The typical 40M beam is a
> > loaded
> > element and on a boom that is usually 20 - 24 ft long. 24ft high is
> > not
> > enough to have the DE up and away from the ground.
> >
> >
> >
> > It will tell you its not shorted or open but as to whether its
> > tuned right,
> > it needs to be in the air.30 to 40 ft up is usually a minimum and
> > even
> > then,
> > the SWR low point will shift by another 20 - 50khz by the time its
> > up at 70
> > * 100 ft in my experience.
> >
> >
> >
> >
> > Ed N1UR
> >
> >
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