[TowerTalk] Guys lines and yagis

[Tom Rauch]

From:           	K7GCO@aol.com
Date sent:      	Wed, 13 Sep 2000 18:17:16 EDT

>  Tom:  I "very clearly" stated that I ran a series of tests in Eznec with
>  a 7 
> element yagi.  You have not.  It was very very clear that any guy wires
> (even tips of 1/4 wave grounded guy wires) with the tips 1/2 WL from the
> top of the tower were "virtually immune" to the beams field below the
> tower.  It was on a level of what was on a tower with a horizontally
> polarized beam with no RF Spill Over on the feedline.  The computor
> "RFSource" is right at the feedpoint so there is no feedline shield to
> spill over on to.

How many different guy lengths did you model? 

How many different antennas?

Did you vary the length of the guy lines?

What angle were they at? 
 
> Now you state that "its possibly true for small beams (perhaps 2M) spaced
> 'well above' the guys it is most likely correct". 

No, I didn't say that. It is a better idea to cut and repost what I say, 
instead of quoting what you "think" I might have said.

> stated "have the guy wire tips "1/2 Wave Length from the tower connection
> and beam." 
>  That doesn't mean "Well Above."  It's not a "Relative Measurement."  It's
>  a 
> "Precise and Exact Measurement".  Example"  It's about 39" at 2M (small
> beam) and 35' at 20M (large beam).  

I'm not sure what you are saying. 

Are you saying that with guys at any angle and any attachment 
point and length, the guys only need to be 1/2 wl from the antenna  
(and tower) to not affect pattern?


Have you got the "Exact Distance
> Picture"?  It's in "Wavelength."  It's NOT a "General Rule" as you
> suggest.  It's an "EXACT K7GCO RULE" I derived from High Level Computer
> Interpretation.  

Other people may have higher reading skill values than I do. I have 
a difficult time understanding how that rule is "exact". It seems 
vague to me.

How many combinations dod you model?

> If you understood Basic Beam Tuning 101 you would have full knowledge of
> the fact that in order for each director change (and the Rr--that's
> Radiation resistance) to increase gain at less than 1dB (and a bit less
> progressively for each one), they have to be:
>  1.) In the same plane
>  2.) Of the same polarization
>  3.) The right spacing
>  4.) The right length
>  5.) All joints have a "Reasonable Conductivity and a Longevity Factor". 

Filling in or moving nulls is as much or more of a problem than 
increasing gain. It takes only the smallest amount of re-radiation to 
destroy the null of an antenna.

A conductor 100 feet away can easily change the pattern of a yagi, 
as does the earth at that distance and further, on 20 meters.
 
Respectfully, I think your "exact rule" is too poorly defined to be 
considered an exact rule.  

>  If 
> it's not and frequently it's not with yagi's after a time period without
> the right element goop.  It lowers the Q which is like any other critical
> tuning factor in gain and F/B.  When the elements eventually becomes
> capacitive reactive at the joints, it literally neutralizes the other 4
> even if properly adjusted.  

How does the "capacitor" formed in the oxide withstand the voltage 
from the element without breaking down? 

> of each and every element--100% of the time.  Quads have the advantage of
> having "one permanently soldered joint and never detunes" if
> soldered--some aren't.

I've never seen a element joint problem with my yagis. I think that 
problem is a greatly exaggerated problem.
 
> Guy wires 1/2 WL or more slopping away even if resonant do not under any
> circumstances full fill all 5 critical tuning factor requirements.

How do you know? They can be almost any angle, and length. How 
do you know they are non-resonant?

> recommend at least 1 insulator at the tower if metal guys are used full
> length.  Put another one in at say 10' if it makes you feel better.  As
> the gain of a beam increases, the vertical pattern sharpens--that means
> less pattern BELOW.  

I just modeled a 40 meter yagi using you guidelines above, and 
when the guylines are resonant the front to rear null ratio in the 
model goes from almost 40 dB down to ten dB. You seem to imply 
that can't happen, if I understood you correctly.

The beams pattern below becomes progressively immure
> to any specific non resonant object around it except in the front and even
> then it still has to full fill ALL 5 requirements of above.  For example a
> 2 element beam may have a 50 degree -3 dB point above and below where a 5
> or so element may have around 30 degrees or less. 

That is a far field pattern, not a near field pattern. You certainly 
have the right to use a far-field pattern to predict there won't be a 
problem, but you should remember the answer will likely be wrong.

 > correctly adjusted, each director adds less and less gain and has less
> change on the Rr.  Take a 3 element and then a 11 element 2M yagi and move
> a director around it and watch the SWR and S meter.  A 2nd reflector for
> example of the right length does virtually nothing in the back--there is
> the 3nd least field for it to work with.  That's why the Raibeam doesn't
> have a conventional reflector--it design doesn't need one due to it's
> clever design.  That now unused element spacing is used more effectively
> in front with another director for the 3, 4 & 5 element Raibeams.  As I
> have said before, this is the first real improvement to a yagi since 1922
> as it gives absolute maximum gain for the length of the boom.  The Raibeam
> also holds it's pattern and low SWR over a wider frequency.    

A Raibeam is simply a two-element phased driven array with 
optional additional directors.  I had a similar antenna on 40 meters 
in the 80's. It has high f/b if adjusted correctly, but basically no 
more gain than any yagi on the same size boom.  

One model does not verify a "rule", it only verify's the one 
circumstance modelled within the limits of the model.

I deleted the rest of the talk about baluns (and a few personal 
snipes)  because two or three topics in one post are enough.

So tell me, how many cases did you model to confirm your 
K7GCO rule always works? Can we expect other tower owners to 
go out and remove the insulators breaking up their guylines with no 
ill effects, as long as those guy lines are 1/2 wl from the antenna 
and tower?'




73, Tom W8JI
w8ji@contesting.com

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