What you describe leads me to believe that your sloper is not working as it
should. I run 4 slopers on each band (40/80/160) around my 100 ft tower
which has a C31XR on top. The slopers are selectable via a remote switch.
They give some gain and direcectivity in the direction of the slope. Mine
are pointing NE SE SW and NW.
My experience having used this type of array at 3 different locations over
the past 30 years is that each sloper will be a bit shorter than what the
formula calculates. I have also found that the angle at the apex should be
at least 60 degrees if at all possible. That puts the low end a lot further
away from the tower and a lot higher off the ground than yours. In my case,
I used elevated posts (12 feet high) about 125 feet away from the tower and
tie each of the 3 slopers per post off to those non-conductive wooden posts
using uv resistant rope.
To run multiple slopers on multiple bands requires some effort to get each
one tuned, but using an MFJ it isn't a major undertaking. Once tuned they
work great. On 40 meters I can stay below 2:1 for about 200Khz. On 75
meters (I tuned mine for 3800 Khz) the 2:1 bandwidth is about 60Khz and on
160 (tuned for 1845 Khz) it is about 40 Khz.
For those that wonder about the directivity and gain i can only say that (as
but one example) there have been lots of times that I've tried calling DX
stations and the ONLY sloper they can hear me on is the one pointing
generally in their direction. I can sure tell the difference on receive as
well.
Jerry Boyd
N7WR
>From: "Dale Martin" <kg5u@hal-pc.org>
>To: <towertalk@contesting.com>
>Subject: Re: [TowerTalk] 40 meter sloper question
>Date: Tue, 10 Oct 2006 10:44:28 -0500
>
>
> > Hi Kirk: My understanding is that a sloper working against a
> > tower is a sort of dipole with the tower as one part and the
> > wire as the other. I have found that the sloper usually must
> > be greatly different in length than 1/4 wavelength to achieve
> > a low SWR. The tower is very much part of the radiator. I
> > think your tower is the main radiator and the sloper is a
> > matching system which does very little radiating. I think you
> > have a good system of loading your tower at present.
> > 73, Dan, N5AR
>
>Also, isn't whatever beam(s) you have on the tower top a significant
>factor,
>acting as a tophat?
>
>I noticed when I changed out a TH6 (damaged) for an A3 and later for an F12
>C3E the my 80m 1/4-wave half-sloper was affected. I don't recall if I had
>to lengthen or shorten it, but it did make a difference.
>
>My sloper feedline and antenna node is on the very top of one of the legs
>of
>my Rohn 25G pointy-top where it slopes to meet the mast tube.
>
>Maybe that's Kirk's problem. His quad is not acting as much as a tophat
>for
>the sloper as a beam might.
>
>Kirk: I have heard of people extending a mast high enough above their
>beam/quad for a wire antenna to clear. It's bizarre and I don't know if it
>really works, but might be worth a look.
>
>
>73,
>Dale, kg5u
>
>
>
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