[Towertalk] 15M on C31XR

[n4kg@juno.com]

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
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________
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> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk


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