[TowerTalk] TEK screws

K7GCO@aol.com K7GCO@aol.com
Sun, 19 Mar 2000 17:33:53 EST

   I have thought of other considerations in the use of TEK self tapping 
screws in addtion to the ones below.  As staed below, if you wnat compression 
between 2 tubing for RF conduction, the hole in the outter tubing has to be 
larger.  This means that the screw is threading into a .058" wall or less.of 
the smaller tubing and is easy to strip.  Therefore it's a good idea to add a 
narrow ring of smaller tubing inside for the TEK screw for at least 1/4" 
total of thread grabbing.  Be sure to buy TEK screws that are 3/8" long after 
the pointed area--get 1/2" and SS if you can.  Coat hole and screw with 
Silicone grease before and after installation.  At best it gives a localized 
PRESS fit for RF conduction that will be stronger than hollow pop rivets.  
The closer to the end of the larger diameter tubing the better for the least 
RF resistance long term if coated.   I've used all these Band-Aids for years 
and this screw will hold with 1/4" of grab area.  But a SS hose clamp on the 
end of split tubing well greased still gives the best no compromise low 
resistance connection of all if coated--right at the critical "thin ring of 
connection" at the diameter change.  

All these problems just GO AWAY when two wires are twisted and permanently 
soldered--one per element.  There is a beam antenna that uses this highly 
advanced concept of Longevity Antenna Design.  Wire is pennies/ft compared to 
aluminum to do the same job, long lengths of wire are easy to ship without 
UPS restrictions and there are no "Press Fits" except at the feedpoint (which 
can be soldred) in a properly designed antenna.  In case you have forgot it's 
called a QUAD.  I check the resistance path of the DE at the end of the feed 
line and record it.  If that stays the same there is no electrical 
deterioration.  It stays at 100% effectiveness day after day and year after 
year.  No other antenna can make that statement in the Antenna Kingdom except 
the HexBeam.  Yagi's with a very tight compression fit at each joint properly 
coated will do the job also. If you ever take a yagi down, check the joints 
with an ohm meter.  

I installed a 12M yagi 6 months ago just for a months use.  I didn't coat the 
joints.  The great F/B ratio it had has vanished.  There are a lot of unoated 
beams out there that need a cleam job and coating.  I'd use the grease that 
has aluminum particles in it--not zinc which is a dissimilar metal.  k7gco

In a message dated 17.03.00 13:18:12 Pacific Standard Time, K7GCO writes:
 Yes the TEK screws work.  But again it is a dissimilar metal--1 of the three 
corrosion creators along with air and moisture.  I coat the hole and screw.  
Make sure the inside hole drilled is the right size for the self taping 
screw.  Insofar as a 1/4" TEC being long enough for 2 layers of tubing 
(1/4"), examine the screw and make sure the tapered area on the tip is 
through or they can work out again.  The hole in the outer diameter tubing 
should be larger so the grip in the inner tubing can compress it to the outer 
tubing for better connection and rigidity.  To be sure get a 3/8".  Hy Gain 
used to use them and they were long enough to go through and they used lock 
washers to help anchor it.
 The lose fit of the tubing (what is the wall thickness of the outer tubing?) 
apparently led to the rivets being all in a row which limits the contact area 
of 2 round objects of different diameter.  Instead of 360 degrees of contact 
area there is perhaps 10-20 degrees and it mostly just at the diameter change 
where the RF makes the jump.  The TEK screw idea at 90 degrees is great to 
anchor it wiggle wise but more rivets would do the same and they aren't a 
dissimilar metal.  Grease the hole and rivet.  It also increases the contact 
area to over 90 degrees but only at the diameter change.  I like a tight 
coated clamp on coated joints that gives 360 degrees of contact.  
Psychologically it gives a lower resistance fit also.
 Properly designed quads don't use rivets or Penatrox on the one wire 
connection (just plain solder) per element, don't need rebuilding, all the 
delay and crane fees. The electrical efficiency of quad element connections 
remains at 100%--permanently!!  Longevity of design is minimized to reduce 
cost and appeal to the "tight budget ham" of many products.  They will pay 
far more in the end.  I have a Collins KW-1 and a 75A!.  In 47 years both 
have only had one component replaced or more than one hour down time.  In 
Quality Assurance that's called a "Robust Design."  The Zenith Radios of the 
30's are still working 65 years later.  
 I have made arrangements for a Special Oven in Hell for those "Tight Budget 
Mfgs" and another Oven for those who buy from them.  Would you believe they 
still do business with each other down there for air conditioners and other 
hot products.
 K7GCO >>

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