[TowerTalk] TEK screws
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
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