[TowerTalk] (no subject)
K7GCO@aol.com
K7GCO@aol.com
Wed, 13 Sep 2000 18:17:16 EDT
In a message dated 9/12/00 7:55:15 AM Pacific Daylight Time,
> w8ji@contesting.com writes:
From: K7GCO@aol.com
Date sent: Tue, 12 Sep 2000 00:05:26 EDT
Subject: Re: [TowerTalk] Re: my Phillystran question
To: to wertalk@contesting.com, ndavis@vt.edu
> Computer test show you only need 1/2 WL of Phillystran form the tower
> down to isolate the beam from any affect of the guys from there on down.
> On 20M use 36' Phillystran guys starting at the tower. The lower metal
> guys can be a 1/4 Wave on 80 or 40 depending on the tower height with
> radials around the ground tie point. Put the guys to work. K7GCO
This depends on the size of the antenna, and the pattern of the
antenna. With small directional antennas, spaced well above the
guy lines, that statement is most likely correct.
It should not be used as a general rule in all cases.
What you want is the guy line out of the field of the antenna, so
there are many cases where the suggestion above won't work.
73, Tom W8JI w8ji@contesting.com
>>
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.
Now you state that "its possibly true for small beams (perhaps 2M) spaced
'well above' the guys it is most likely correct". Tom, I very clearly 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). 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. It's
very clear. If you understood the relative pattern amplitudes of the
VERTICAL PATTERNS below a beam you could understand this. Whatever reduced
radiated RF below a beam is in dB from the main lobe, any reflected RF from
guys or other beams is reduced by the same number of dB in detuning and the
other factors.
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". 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. "All 5 factors" have to be carefully maximized 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.
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. I
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. 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. Even when a director is 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.
I've given this demonstration at Conventions and Clubs. I'll dig out a
detailed Post on this. RF spill over causes SWR and pattern changes like
from TA-33's and dipoles fed without a balun. It's very low or no gain broad
vertical patterns can cause detuning problems from metal guy wires in
particular without an insulator at the tower and changes when rotated also.
The "Dreaded RF Spill Over" is another source of undesired radiated RF that
brings the tower and guys into the picture that has not been properly
addressed. F/B is ruined even without any guys wires and more vertically
polarized noise is picked up also. Low gain antennas like this fed without a
balun probably brought this potential problem to light and has been carried
over to beams that don't deserve this "guy wire curse." I like 2 element
beams, use them all the time but they require "clean feedlines" to prevent a
reduction in F/B and SWR changes when rotated with metal guy wires without
insulators. I seem to be a "lone voice" in this "Public Service Information
Area" except for an article in a 1938 Radio Mag by Bailey and a 1952 QST
article on a 2M collinear vertical by Remington Rand (the Shaver guy). For
those manufactures who's beams have the proper "RF Spill Over Free Matching
Systems" accidentally or on purpose, none have realized the sales and
performance advantage of it and advertised it. I'll have to start the "K7GCO
No RF Spill Over Certification Service" on all antennas.
End fed verticals are the "absolute all time worst offenders." There are
ways to reduce that from the mast and coax. Coiling the coax below a high
current beam or vertical feed point is the least effective Band Aid (it's not
resonant--just a small inductance) as the RF Spill Over is still on the mast
also. It is an effective RF choke 1/4 WL lower in the high voltage area
where the increased capacitive between the turns and the proper number of
turns can create a resonant choke tank coil just like trap coils if not
detuned by surrounding objects in it field and to absorb to it. Even though
it works 1/4 WL lower on the feedline only, it's still radiating for the 1/4
WL distance. When properly used I call it the "Truman Choke"--the RF Spill
Over stops here. Whoever came up with choke coil idea in the high current
section should be hung with it. Feed techniques that do not permit RF Spill
Over are the "No Band Aid Way" to design and antenna. I wish I could show on
TT all the patterns I made showing the lack of guy wire affect when 1/2 WL or
more away. Beams with no RF Spill Over and the higher the gain, the more
immune it is to detuning from surrounding objects--even in the main lobe.
Once radiated and deflected off the main lobe in the far field, RF can go off
in the wrong direction, however. I plan to publish an article on this along
with scale model data.
30 years ago Dr Don K Reynolds of the U of Washington did a scale model guy
wire test and found the same thing. I saw the data. So has Lou Gordon K4VX.
He is a competitive DXer who is always looking for "Stray RF", has several
stacked arrays and even created his own Antenna Software to check out things
like this. You are all alone Tom on this one with your views. You have
absolutely no competition in finding picky fault with hard cold data without
any of your own. Give us a Break Tom! If you got something that is original
and not picky lets hear it.
Just what do you base the last 2 sentences of your statement on? Tom: Don't
you ever get tired of being wrong? I like being on the safe side all the
time, like self supporting towers and telephone poles but wearing a belt and
suspenders to support you "opinion" here is a bit of over kill when the
computor and scale models show it's not necessary as I specified. Spend some
time with Eznec and on the test range with a 3 and 11 element 2M beam with no
"RF Spill Over" (the Cushcraft 11 element has a gamma which I changed to a
200 ohm "Balanced FD" to eliminate excessive RF Spill Over--1/8" extra feed
wire 2" below existing DE) on the feedline and an extra director or the
equivalent of guys wires as suggested above. Try scaling a 20M tower with
guys on 2M.
Everyone is entitled to their "Gut Opinion" but many of yours needs a
"Technical Colonic." Most of your opinions--smell. I respect and welcome
them all from you and everyone but this one "served no useful purpose
whatsoever" other than to express you opinion which had no data to support it
as usual. I'll send you my Eznec file and you can see it in there also along
with any other data you would like. Your "Where's The Wendy's Technical
Meat" was again missing. It was an all "Dried Out Empty White Bun" without
any Ketchup or Lettuce--just Sour Opinions oops--I mean "Sour Onions". If
you got some "Data Meat" please send it to me and perhaps I'll eat some Crow
or at least share of bottle of "Old Crow" with you. I require "Filet Mignon
and all the Trimmings" for Technical Data discussions to hold my attention.
Then I'll listen to even you. K7GCO
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