[TowerTalk] Guy Wire Affect On Beams

[K7GCO@aol.com]

There has been more comments about breaking up guys wires.  I wrote the 
following some time ago.  Barry k8bk came up with a solution on how to solve 
the problem.  I verified it in Eznec and the findings are below. 
 
In a message dated 01.05.00 04:51:57 Pacific Daylight Time, 
k8bk@speedconnect.com writes:

<< I thought I had sent this before but I will try again.  I have a quick 
question.
I am putting up a new C4SXL antenna on my 75' Rohn tower.  I am wondering if 
it is worth it to run about 50' of Phillystran off the top of the tower then 
finish with regular guy wire.  Is 50' worth the expense?  I will be running 
my 80 and 160 antennas out of trees so I have no plans of running other 
antennas off the tower at this time.  Thanks de Barry/K8BK  >>

Barry: That is a great idea.  A couple months ago (and some now) there was a 
rash of posts all concerned about the affect of guy wires and insistence of 
insulators every 13' or whatever.  It sounds logical.  Howsomever.

I modeled a tower, guy wires and beam in Eznec and found exactly what I had 
expected.  My recommendations from actual observations for years has been to 
use Phillystand originating from the tower for a 1/2 wave of the lowest beam 
frequency. Then you can use even resonant wires from there to the ground like 
a 80 or 40M ground plane originating at the ground guy point if the tower is 
high enough.  The tower can give some gain affect also

With continuous guy wires connected to the tower, I found very little RF on 
them for the lengths I used.  Other more resonant lengths may have absorbed 
more RF thereby upsetting the beams pattern and Z far more.  A tower 
connection point just 5' below say a 20M beam can have some affect with 
80-40M inverted vees.  One can easily see relative amplitude of the current 
loops on guy wires or inverted vees in Eznec--and the current values are 
recorded in Eznec at any point on any wire.  I can amplify it many times so 
as to see very weak levels of the current loops in Eznec.  I did a full bore 
amplify to where the current loops of the beam elements went out the top of 
the screen literally all the way to the ceiling before any RF current could 
been seen on the guys connecting about 5' below a 20M beam.  So much for 
insulators in guys.  

In the Eznec test there is also no RF Spill Over on to the coax shield as 
there isn't any feedline connection wires in the antenna field.  It's like 
the transmitter is right at the feedpoint.  I have added them to simulate 
unbalanced coax connected to a balanced feedpoint to show what happens in 
actual practice.

First off if you have no change in SWR as the beam is rotated, one could 
basically ignore the guys although at least one insulator at the tower will 
prevent the "Dreaded RF Spill Over" from going down the guys but not the 
tower.  If there is some change you have to decide if some surrounding object 
is the cause or it's reacting with RF Spill Over.  Add a balun and recheck.  
One main cause of SWR change with rotation is when a beam like the TA-33 is 
fed without a balun.  The coax shield is hot with the "Dreaded RF Spill Over" 
and that really excites the tower and guy wires to where you can see a SWR 
change with rotation and lowered F/B.  That problem has never been fully 
recognized.  Adding insulators to the guys can eliminate or reduce the affect 
but NOT THE CAUSE!  Solution: Add a balun or use a beam that doesn't need one.

I then added guys to the tower in Eznec that extended to within 1/2 wave of 
the tower.  I increased the amplitude full bore of the current loop and the 
shortened guy wires were literally stone cold.  There is nothing in the beams 
field to get excited about--or excite.

Consider this.  Lets take a 3 element yagi.  It has a directive vertical 
pattern in the field of the guys which limits the amount of RF they see.  If 
RF is reflected back at the beam, the directive pattern again limits the 
amount it sees in return to upset the beams pattern and Z.  If you add 
another director it sharpens the vertical pattern even more which limits the 
guys or other objects affect even more on and on.  It's the low gain beams 
that sees more of the guy wires.

Now consider this.  In order for the additional director to squeeze almost 1 
dB more gain, here is what has to happen.  This director has to be in the 
same plane on the boom, of the same exact polarization, of a specific and 
optimum spacing and an exact length to an inch.  If so it will also change 
the Z but progressively less as the number of directors is added.  As the 
number of elements increases the beam gets progressively pattern and Z 
independent of surrounding objects--even in the front.  In some multi-element 
yagi's I have, the feedpoint Z actually goes up.  I was fully aware of the 
critical nature of these 4 requirements from tuning yagi's manually on a test 
range and in Eznec.  If anyone of the 4 concepts is not optimum the gain 
cannot be maximized.  Even if maximized you will barely get 1 dB gain and 
less as each director is added.  It's easily seen in Eznec and it can be 
scaled on 2M real easy to prove it further which I have done for talks.

Now this being the case all those who lost all that sleep over breaking up 
guys have never tuned a beam manually with no RF Spill Over on to the coax 
shield, tower or guys or in Eznec.  The guys are not in the same plain, the 
right polarization, the right spacing or the right length.  Not any of the 4 
factors that must be fully maximized is anywhere near.  Without RF Spill Over 
on to the guys, tell me how they are going to affect the beams pattern to get 
all concerned about.  A good rule of thumb is if the guys or horizontal wires 
are no closer than 1/2 wave from the beam and below it, it for all practical 
purposes is pattern interference free of these objects as I see it in Eznec.  
The tower does have a little RF on it but this is unavoidable even with a 
clean feed system.  This RF can be removed with some 1/4 wave stubs connected 
to the tower at the right spot--1/4 wave below the beam pointing down.  I 
call them "RF Trick Sticks" or "RF Tower Cleaners."  
 
I had a TH4 on my tower with a balanced feedpoint fed directly with coax.  
The SWR changed as it was rotated.  I blamed it on the power lines 50' from 
it at the same height.  I added 2 RF ammeters in the feedpoint and recorded 
their values every 30 degrees.  They read like one at 3 amps and the other 4 
amps due to RF Spill Over and varied 20% as I rotated the beam.  The coax ran 
20' down and then parallel to the beam for 15' and then down again.  RF was 
induced on the shield more or less as the beam was rotated and it affected 
the RF currents in the feedpoint and SWR as the beam was rotated.  

I added the Telrex balun and the currents balanced within 5% or right on and 
the SWR hardly changed at all with rotation.  RF currents induced on the coax 
shield parallel below were isolated from the feedpoint by the balun depending 
how good it was.  I think the power lines in front may have had some small 
affect along with the power and telephone lines that came from the poll to 
the house.and the slopping ground high and low around the house.  I didn't 
worry about it from then on because I couldn't change it.  I had rope guys on 
this 20' wooden tower on the house. I had a great signal with the balun 
through the power lines in front of the house and the ones in back about 100' 
away.  When I got the TH4 new and installed the balun, 20 M was open to 
Europe that night.  I filled 2 log sheets with consecutive DX contacts--right 
through the horizontal power lines the same height and polarization 100' 
away.  HyGain printed the first log sheet with my testimonial as an 
Advertisement.  So much for power lines.  Barry do you see how good your idea 
is now?  Case closed.  

If Attachments could be sent I could show the relative values of RF current 
on the guys.  The actual values of RF current at anyone point on any 
conductor are given in the Eznec.  As a minimum I'd use a guy wire insulator 
at the tower and about 12' lower for 20M.  For "Totally Adequate Isolation" 
run Phillystrand for 1/2 wave and then steel guys to the ground of any length.

I have all these patterns from Eznec and am writing this all up for one for 
the mags.  I still have all the data I took on the TH4 feedpoint currents 
before and after the balun was added.  It was all printed in a book I wrote.  
If I can get this letter Scanner I have working I can put it on TT.  I hope 
this all sheds some light on the affect of guy wires.  With stacked beams, I 
will put in Eznec the equivalent of what guy wires in front of a beam do.  
I'd use Phillistrand and then never have to worry about it.  During the mean 
time, use beams and feed systems with no RF Spill Over.  Get the Palomar RF 
Current Meter and measure it.  I think CQ just had an article showing it.

Too many get too concerned or what sounds right rather that what is really 
right.  Take a 2M beam and another director and move it around a 2, 3, 5 &10 
element beam.  Do it with stacked beams.  Connect guy wires with and without 
insulators.  Observe the SWR change--if you can see it.  Use Phillistrand 
guys for 1/2 WL below the beam and then wire.  Do it in Eznec also.  This is 
another reason I like telephone poles.  It's easy to take RF off coax and 
rotator cables and create a very clean mounting for a beam.  Case closed.  
K7GCO

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