[TowerTalk] F12 C19XR Rivets

[Jim Thomson]

@@@  Stainless steel does not conduct RF  worth a damn.   F12 uses 12-24 SS 
screws
to make the balun connections... between a pair of SS nuts and SS 
flatwashers.  I also tried the same
stunt, using SS for connections to a vac tune cap, bad news.   Where RF has 
to flow through a screw,
brass, silver plated brass, or phosphor bronze screws works a lot better. 
But we are talking about using screws
to mash two surfaces together, in which case, anything will work.   F12 
tried using 8 ga  SS solid wire to make the
hairpin coil on a 40m yagi, more bad news.  The coil turned black, dead 
center in the middle of the coil, where
the current is highest.    For a laugh, I tried  SS  8 ga SS solid wire for 
a 40m tank coil in my hb linear, what a disaster.
Also tried AL  tubing, like the soft 3003-H0 alloy, for a 20m tank coil, in 
the same linear, also with disastrous results.


@@  Im not about to replace the solid al rivets on any of my f12 yagis  with 
SS self tapping sheet metal screws anytime soon.
f12  puts the 1st rivet almost at the end of the joint, close to the edge, 
( too close, it should be 1.5 diameters away from any edge)..
so no way to install a SS hose clamp.  Hose clamps  wont even work unless 
you have at least one slot cut into the outer tube.
So its either rivets, ss self tapping sheet metal screws... or slots + SS 
hose clamps.   If slots + hose clamps + screws used,
the hose clamp would have to be cranked down good and tight..1st, b4 any SS 
self tapping screws being installed.

@@  SS machine screws + SS nylocks.... at right angles to each other, will 
also work good.   Bottom line is, use whatever
works for you.  If starting from scratch, then you have more options.  BTW, 
for you folks that buy AL tubing from DX eng,
they now offers  AL tubing with NO slots on either end.  b4, DX eng sold 
their tubing with  4 x slots..a slot every 90 degs,
on ONE end only.  Previously, if you didn’t want to use the slots, the tube 
was flipped 180 degs, so the slotted end
was stuffed into the next bigger tube...never to be seen again.   The 
advantage to the... no slots at all option, is the
tubing is now even cheaper to buy.  EG:  .375 OD  x .058 wall  x  3 ft 
long, is only $1.48  ( 6063-T832 alloy, which is the
same 40 ksi yield strength as the more expensive 6061-T6 alloy).    Yield 
strength X section modulus = bending moment.

Jim   VE7RF


-----Original Message----- 
From: Bert Almemo
Sent: Tuesday, March 08, 2016 9:09 PM
To: 'Jim Thomson' ; towertalk at contesting.com
Subject: RE: [TowerTalk] F12 C19XR Rivets

Jim,

While I agree with most of you're writing I think you'll be hard pressed to
get a solid 9 square inches of surface contact in your 1 inch tube with 3
inches of overlap.  Maybe if you put in a lot of SS screws or rivets at the
joint. If you're using any kind of joint compound, like Penetrox, you need a
certain pressure to make a good contact, as I'm sure you know. SS hose clamp
+ SS screws has been a good combination for me.

Bert VE3NR





-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
Thomson
Sent: Tuesday, March 08, 2016 10:46 PM
To: towertalk at contesting.com
Subject: [TowerTalk] F12 C19XR Rivets

Date: Tue, 8 Mar 2016 15:22:32 -0500
From: "Bert Almemo" <balmemo at sympatico.ca>
To: "'Roger \(K8RI\) on TT'" <K8RI-on-TowerTalk at tm.net>,
<towertalk at contesting.com>
Subject: Re: [TowerTalk] F12 C19XR Rivets

I learned long time ago that using pop rivets, blind or not, don't make for
a good electrical connection. For all antennas, using aluminum tubing, I've
used self tapping screws for the last 30 yrs and it's served me well. It's
also much easier to take antennas apart and put them together again using
screws. As always, OMHO!

73 Bert, VE3NR

##  The electrical connection is between the mating aluminum tube surfaces,
not the  rivets/
self tapping screws.   A  1 inch OD al tube, with say a 3 inch overlap, will
have 9 square
inches of surface contact.   Unless the self tapping screw is SS, it will
rust.  If it is SS, then
you have the dissimilar metal issue.   Mosely etc, uses  SS  self tapping
screws, and they work
just fine.   Heck, I used a single slot + SS hose clamps  for several years
on my hb yagis...and
they worked just fine, with 100% of the RF flowing through the mating
surfaces.   Hy-gain, wilson
etc, used those compression clamp assys....which I just hate with a passion.
Local fellow here had a
hy-gain 204BA  up 100 ft near a cliff edge, and after a few years, some of
the tips and inner sections
were just about ready to pop right out.  They had migrated outboard quite a
bit.   Same fellow also
had the old KLM 4 el 40m yagi......and it self destructed.   It was new at
the time.  He ended up
buying a bag of SS  self tapping machine screws, and drove em in everywhere.
Problem solved
with the ele migration problem.  Next problem was the KLM 40 eles came right
off the boom.
The 'fix'  for that was to use multiple SS hose clamps to hold the lexan
brackets to the boom.
Then drive SS self tapping screws through the slots on the SS hose clamps.

##  I have never seen  SS self tapping machine screws ever loosen up, they
seem to hold stuff
together quite well, just don't  crank em in too tight, into al tubing,
such that they strip out.

Jim   VE7RF

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