That reminds me of a situation described to me by a friend.
He had an A4S at 70 ft and noted it worked well on 10 and 20
but seemed less competitive on 15M.
I asked about his guy wires which were placed at 30 and 60 ft.
The KEY was that his first insulators were 10 ft from the tower.
That effectively placed a 15M director 10 ft BELOW the DE !
(10 ft guy + 1 ft of tower width + 10 ft guy = 21 ft which is
just about right for a 15M director).
The First Insulator needs to be as close to the tower as possible,
(less than 4 ft) with the second insulator less than 0.3 WL away
on 10M (11 ft) to prevent strong interaction. I like at least 2 guy
sections 11 ft long between insulators close to my high band
antennas.
Tom N4KG
On Wed, 8 May 2002 "Mike Fatchett" <mike@mallardcove.com> writes:
> Is there anything else on the tower other than the c31? This sounds
> like an
> interaction problem. What kind of guys are on the tower. Are there
> other
> antennas close by? Does the SWR change as you rotate the antenna?
>
> Just a few questions.
>
> Mike W0MU
>
> -----Original Message-----
> From: towertalk-admin@contesting.com
> [mailto:towertalk-admin@contesting.com]On Behalf Of
> mwdink@eskimo.com
> Sent: Wednesday, May 08, 2002 12:31 PM
> To: towertalk@contesting.com
> Subject: [Towertalk] 15M on C31XR
>
>
> Hello All
>
> Since the talk about antennas and towers seems
> far and few between lately, I'm gonna throw
> something out for reflection. I've tried
> asking this on the Force12 reflector a
> couple years ago before but didn't get
> much response. Since this antenna is even
> more wide spread now, Steve suggested I
> try it over here. (I also figure
> ALL of them are over here plus more.)
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
>
> I have a C31XR. I'm quite happy with it but I
> get the "feeling" 15M isn't playing as well as it
> could. Yes!, that's a really hard thing to quantify.
>
> 1) The antenna's SWR on 15M reaches it's minimum
> between 20.0MHz and 20.3MHz. I just use a tuner
> to make the rig happy. I know that SWR is not the
> be all and end all but I know the expected minimum
> SWR for the antenna design is higher up the band.
>
> 2) After several years of competition, I just keep
> getting the heck beat out of me on 15M. (I feel
> competitive 10M and 20M.) When others in the area
> have high Q totals on 15, mine are always mediocre.
> I do accept the possibility that I may just be a lousy
> contester too.
>
> No, this is not a case of adjusting the infamous
> parallel wires, this antenna is feed with 3 separate
> feedlines (though I am tempted to go to one feedline
> just to see if things improve). I am well versed in
> all the ONE feedline techniques but it's not the
> same beast.
>
> Yes, I have made all the changes in the
> instruction book (moved driven element back, different
> hairpin coil, shortened and lengthned specified elements,
> etc). I have rechecked the measurements until I am blue
> in the face. I have made sure the tubing is going the
> right direction (an easy mistake if not careful).
>
> Last summer, I had it down and played with the driven element
> length just to see if I could raise the frequency at
> which the SWR bottom out. (I realize I may have messed up
> my gain and f/b but it was an experiment). I got it
> where I wanted it at ground level (about 20') but as
> soon as it went back up the tower - same result, back
> into lower 20MHz region.
>
> So, I am looking for someone else with the same antenna,
> feed with 3 feedlines, who may have experienced a similar
> situation and solved it. It's not intolerable, the antenna
> (at 100') works and it beats a C3S I have at 40' - it just
> doesn't seem up to par with the other bands.
>
> I thought I would throw it out and see what floats up.
> Give us something to think about beside viruses and
> insurance. :>) (NO criticism intended on ANYBODY)
>
> 73
> dink, n7wa
>
>
>
>
>
>
>
>
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>
>
> _______________________________________________
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