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Re: [TowerTalk] Length of Sloper?

Subject: Re: [TowerTalk] Length of Sloper?
From: "Roger (K8RI)" <>
Date: Wed, 29 Dec 2010 22:26:10 -0500
List-post: <">>

On 12/29/2010 6:59 PM, wrote:
> Hi Guys,
> I'm installing an 80-meter Sloper on a self-supporting 60'  tower.  (no
> guys)  I don't have a MFJ-259 or other antenna bridge  with me so I'd
> appreciate your thoughts to help get me in the ballpark.   The 80-meter 
> Sloper will
> attach to the tower at the 55'  level.  Currently there are no other antennas
> on the 60' tower.   A couple questions:
 From the description I'm assuming you are referring to a "half 
sloper".  I use one on 160 through a tuner) and it works just fine.

I use half wave, center fed slopers on 75 and 40 and they too work 
fine.but again I feed them through tuners and use current baluns on 
five, 2.4" OD 32 mix cores.
> 1) With no other antennas on the 60' tower, do you think the length of the
> Sloper wire will be close to the formula 234/freq?  Or do you think  the
> Sloper will wind up needing to be  longer or shorter than  234/freq?
It really doesn't need to be resonant.  The antenna will radiate all the 
power you can get into it.  Ideally a tuner at the antenna feed point of 
the half sloper is the way to go, but if coax fed without a tuner then, 
yes it will likely need to be shortened with the addition of antennas up 
Will it be close to the frequency?  Yah, kinda, sorta, probably... The 
formula is normally good for getting you close.  I've never cut one to 
formula yet that didn't require pruning, so I just make 'em longer than 
necessary and prune.  I do aim for resonance in the bands because that 
gives me a bit more leeway where I can move up and down the band a ways 
before I have to retune. On a single wire, that is not far.

I've taken to adding a second wire with a 3 to 4 foot spreader at the 
far end. This lowers the Q substantially.  With that kind of separation 
some cut the two wires for different parts of the band.  This works 
quite well on 75 and 160 and should work equally well on the 75 meter 
half sloper and *might* make it easier to match. However the capacitance 
of the second wire to ground will require shortening it a bit.

> 2) The once I get the Sloper tuned for minimum SWR on 80-meters, if I later
>   add a Tribander to the top of the tower I'll no doubt need to re-tune  the
> Sloper, but do you think the Sloper will need to be shortened or
> lengthened after the Yagi is added?
If feeding it through a tuner I'd not worry about it.

73 and good luck,

Roger (K8RI)
> Thanks&  73,
> Dick- K9OM
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