[TowerTalk] (no subject)
K7GCO@aol.com
K7GCO@aol.com
Thu, 14 Sep 2000 12:50:52 EDT
In a message dated 9/13/00 4:34:23 PM Pacific Daylight Time,
w8ji@contesting.com writes:<<
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 computer
> "RF Source" is right at the feedpoint so there is no feedline shield to
> spill over on to.
How many different guy lengths did you model?
*******4 Grounded Resonant 1/4& 5/8 WL and ungrounded 1/2 WL guys that ended
up 1/2 WL from the tower with a 3&7 element 10M beam as they had the best
chance of absorbing RF from a beam at some different orientations. I just
don't have the time to do it for 4 of them over 90 degrees at 1 degree steps
in Eznec. I did it with the 2M beams real fast. It should scale on the
lower bands. I presume that was a good test. If it's not do it yourself.
How many different antennas?
****Count them.
Did you vary the length of the guy lines?
****Read the 1st sentence.
What angle were they at?
*******45 degrees
> 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.
*******You do it all the time to me and others so I thought I would see if I
could slip the (2 meter) possibility past you--for clarity. I was very
specific. Out of curiosity what band were you possibly suggesting? Since
you said it's possibly true for small beam"--what did you have in mind for a
distance greater than 1/2 WL?
> 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. (?)
*******39" on 2M and 35' on 20M are about 1/2 WL (Wavelength). Here is how
you calculate it. Example 492/14.057 MHz=35'. You try this one and tell me
how far I was off. 492/146=??? I thought you would catch it. What is it
about a 1/2 wave you don't understand?
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?
*****Good point Tom. I didn't try it closer than 45 degrees. It should be
obvious
that the closer it gets to the tower the more it assumes the structure of the
tower--and the least possible affect and absorbtion. As the guy wires with
the tips 1/2 WL from the tower are increased in angle above 45 degrees they
get out from the field underneath and are 1/4 WL from the tips of a dipole
and less from the elements of a yagi. There are angles where any coupling
would be zilch. Since no one but maybe you would run a guy wire horizontal
or worry about it--you scale it in Eznec.
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.
******** A half wave is a 1/2 wave, is 1/2 wave, is a 1/2 wave. Review the
math above.
How many combinations dod you model?
*******Covered above. If not enough do some different lenghts yourself.
> 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.
*******That's true but if a null is over a guy--how much RF is going that way
at maximum and how much is coming directly back of the right orientations to
have any affect at all? It is true that resonant objects (with enough
orientation clout) can affect a pattern some not directly in line. The over
all pattern is the summation of all factors. A director can have a big
affect on the F/B. For maximum gain change less than 1 dB for each drector
It takes the beams full frontal gain lobe in line into these directors.
Nulls don't have much clout to create a pattern change. It tends to reject
what little that comes back also.
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.
*****Tom a director or object to affect gain has to be a certain spacing and
all the other requirements. I stated that objects in front of a beam further
out will affect the ground reflection pattern but not the free space pattern
or the DE Z (Driven Element Impedance). Experiment with the 2M beams I told
you to and you will ask better questions.
Respectfully, I think your "exact rule" is too poorly defined to be
considered an exact rule.
******Frankly I couldn't care less.
> 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?
******You ask it not me. I pulled some elements that had been together for
50 years and the Aluminum Oxide (Alumitoid Yagititus--Terminal Case) had
increased the diameter on the inside tubing .015". It was a very very tight
fit requiring a special "jack hammer technique" to get the joints apart and I
saved all the aluminum now worth about $1000 if I had to purchase it. It
tested capacitive before disassembly and the Aluminum Oxide coating was very
clean. The SWR was high and never flickered. I could only get about 20W
into it due to the high SWR so that lowered the voltage potential
substantially at each joint. There was very little F/B where it averaged 30
dB+ around the back with clean joints 50 years ago and after cleaning. Even
if the capacitor arced through that's still a bad connection.
> 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 an element joint problem with my yogis. I think that
problem is a greatly exaggerated problem.
******You probably didn't recognize it as the affects are gradual and slow.
F/B is usually the first indicator and then a SWR change. These joints
didn't have any goop on them and it's a worst case. I made believers out of
some DXers and they clean before every contest or antenna tests as I do. To
eliminate that I came up with the Flea market solder that works great and now
I have "ZERO MAINTENANCE ELEMENTS" going on 7 years. The biggest
"exaggerated problem" really is getting you to do some hard cold hard
research you can understand and if possible review their data before you
literally call them a liar.
> 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?
******Review the "5 orientation statements". Since the lengths are known we
are back to basic math. 492/ft = MHz (1/2 wave). I used 4 radials of 3
resonant lengths in my tests.
> 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.
****That was another test to see if I could get you to do some research in
the Computer. However I would like to see your data.
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.
******Says you. I'll repeat it again. Play with the 2M beams and prove it
to your self as I did.
> 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 3rd 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.
*******Since you haven't actually measured it on a range how would you know?
One model does not verify a "rule", it only verify's the one
circumstance modeled within the limits of the model.
****That's true so I used the worst case--3 different resonant guy wires. I
think even you would admit non-resonant wires would have far less affect.
Would you? I'll forgive you if you do. You know at times I've had the
fleeting desire to have an eye ball technical discussion with you.
I deleted the rest of the talk about baluns (and a few personal
snipes) because two or three topics in one post are enough.
*****No let's let it all out. We have had many so far and I've been told it
has been very informative and entertaining by many. Even my phone is ringing
with support. I've been on it all night.
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?'
******I've told you a couple of times already (count them) and it's a bad
concept to think someone is going to remove whatever insulators they already
have in the guy wires. I have only suggested having Phillistran for a
minimum of a 1/2 wave from the tower--longer if you want to! Suggest changes
that "serve a useful purpose." Now lets get off this picky guy wire routine.
The case is closed except for more constructive research. I only recommend
and give away what cost a lot of time and money freely what I have found
workable from my extensive data in all areas. It's solely up to the
individual if he wants to try it. Since the price was right--give it some
respect. You didn't lose any money on it. I can get a lot of my stuff
printed, can get paid for it and already have requests for it. I've had over
250 articles printed, given over 450 technical talks at Conventions and Clubs
since 1946 in 3 different technical fields and so far no errors or challenges
except from you. You are free to keep trying but do it privately. Lets keep
the information channels open without your constant reticule if you
disagree--in particular without supporting data. I'll get you up to speed in
no time at all. K7GCO
73, Tom W8JI
w8ji@contesting.com
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