Hello Guy and everybody else
Now that's an interesting possibility I haven't investigated.
I think my coax situation has been unchanged since
I built the antenna because they are rather well secured
to the boom. I've swapped baluns but not feeds to the antenna.
They go to a Heathkit mast mounted antenna switch. Don't
remember if it shorts out unused positions (though I
thought it did) I have another on the ground I can check.
46'5" seems rather a long way for a run to the
mast :>) but it's worth a try. However, as a modeling
note, the DE's are actually separated by quite a bit more
than a foot if you are modeling. The 20M DE is
reachable from the tower, 15 is a finger tip
stretch for my 6'+ friend, and 10M is way out
there. :>)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
BTW, I'm going to use this as a general response back
to everybody. Getting to be too much to respond back to
everyone individually. Lot of neat suggestions - many
I have already considered but I appreciate all the input.
Some comments:
1) I don't think interaction is the problem. Top guys
are Philly, my lower guys are well broken and short
next to the tower (2-3'), and the symptoms remain stable.
I had the same exact symptoms on a different tower
and when the guys were steel. While I do have a homebrew
rotatable dipole I can install under the antenna (currently
down) lined up with the boom, the symptoms are the same
installed or not.
2) I am not really concerned with the SWR - I can
live with it as long as I don't feel it indicates
I messed something else up in the pattern. I think
N5AR's null test may help me decide that. Thanks for a
neat idea.
3) I think I need to investigate Terrain Analysis. Maybe I
just installed it a lousy height (ignoring the SWR - see
comment 2) and the "lack of punch" is simply bad spatial
luck or lousy operating abilities on my part.
4) I like the feed coax length idea. Thanks Guy and
someone in VK land mentioned something similar.
5) On a personal note, in all my years of using this
antenna, I have yet to meet anybody else personally
or through somebody else (like Steve/K7LXC) that
uses 3 feed lines on this antenna. Not even someone
who just says - "Yeah, I got one." That's just a personal
observation - I don't get around much anyway. :>)
I'm sure somebody else is doing this.
Lots of people have other Force12 antennas or the same
antenna with one feed but I have yet to ever talk to
one doing this particular configuration who is willing to
admit it. I just find that interesting.
6) One thing I want everyone to be sure of. I like
this antenna, I have no complaints about Force12
or Nathan (who has answered me everytime I ever
bugged him), and I would buy another if I had
the spare bucks. I just wanted to see if I could get
some ideas "outside the box" and maybe some
input from someone with a similar configuration.
I did get some good ideas. This is a "perceived"
performance issue on MY part (which is probably
faulty) and I am just trying to tweak 15M for
the best bang I can get. It's my weak band for
whatever reason.
I thank you all (and if you have any more ideas - let
me at 'em.)
73
dink
At 08:50 PM 5/8/02 -0400, Guy Olinger, K2AV wrote:
Yeah, except his resonance goes WAY down.
This is a three band hookup, three pieces of coax to three separate
DE's within a foot of each other.
Caution: I find in my modeling of the C31 that what is connected to
the center of the other DE's has an influence.
Exactly what is connected to the center of the 10 and 20 de's (balun,
how much coax, what state is the far end of the coax, shorted, open,
hooked up to transmitter, what.
After that can see if what you have hooked up to the other DE's can
detune you on 15.
If that was me, I would have 46'5" lengths of RG8 to the switch (4
elec 1/2 waves on 10, 3 on 15, 2 on 20) so that the unused DE's were
either effectively OPEN, or in the circuit at their resonant state,
depending on whether the switch was open off band or shorted
respectively.
Anything random other than the 46'5" has the capacity to turn the
other DE's into very close reflectors or directors and do terrible
things to gain and pattern. Add whatever hairpin match that may be in
use and you have some ugly possibilities.
I would SHORT/GROUND the unused coaxes.
I modeled various configurations of that antenna and decided that the
three feedline setup was a lot of worry for very little benefit.
Whether this is a problem depends on whether you took it into account
or not.
After that, something to do with an 80 or 40 antenna, near the top of
the tower.
After that, something about the guy wires (as in N4KG post).
AND conceivably, ALL THREE at the same time.
More info about your setup?
73, Guy.
----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>; <mwdink@eskimo.com>
Sent: Wednesday, May 08, 2002 5:16 PM
Subject: Re: [Towertalk] 15M on C31XR
> I would have expected your 40 ft high antenna
> to be better than the 100 ft high C31XR once
> the band opens.
>
> My experience from my own station and
> N4AR's super station is that 15M antennas
> at 80 and 90 ft SUCK during the day because
> there is a BIG NULL from 12 to 20 degrees.
> LOWER antennas (40 and 55 ft) are almost always
> better once the band (15M) opens up, at least from
> the mid-south (KY, TN, AL).
>
> At 100 ft, your null is from 12 to 18 degrees.
> I like 115 ft - 120 ft for high tribanders. This
> places the second lobe at 15 to 20 degrees
> on 15M (very useful) with the null from 9 to 14
> degrees (filled in nicely by a lower antenna
> at 40 to 50 ft).
>
> Tom N4KG
>
> On Wed, 08 May 2002 11:31:08 -0700 mwdink@eskimo.com writes:
> > 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
> >
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > Towertalk mailing list
> > Towertalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
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