[TowerTalk] F12 C19XR Rivets

Wed Mar 9 19:28:52 EST 2016

I believe welding would destroy the temper and is subject to Hydrogen 
embrittlement, making it likely that the elements would fail unless 
there were a reinforcement inside that would not be heated.  OTOH, if 
they were swedged together?  Like SS in intimate contact with no lube 
they tend to weld themselves.
I have two boom sections where either the inside piece is a tiny bit too 
large or the outside a bit small. They went together kinda tight, but 
the only way thy will ever come apart is to cut the outside one off.
An easier one might be to use conductive epoxy?
I think I'll stick with rivets and screws.

Note, there is one thing that has bothered me about rivets and screws.  
For element strength they need to be far enough back from the end of 
outer tube to prevent the holes from substantially weakening the joint.  
How might this affect the electrical length?

How about a banding tool using 3/8ths or 1/2" SS bands on split tubes.

73

Roger  (K8RI)

On 3/9/2016 Wednesday 6:43 PM, Tom_N2SR wrote:
> If you weld the tubing together, what is the wind rating then? Kind of 
> difficult to get apart, but very little risk of losing electrical 
> contact, rivets failing, rusted screws, etc.
>
> Someone should try it and report their results.
>
> Tom, N2SR
>
>
> ------------------------------------------------------------------------
> *From: * Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net>;
> *To: * <towertalk at contesting.com>;
> *Subject: * Re: [TowerTalk] F12 C19XR Rivets
> *Sent: * Wed, Mar 9, 2016 7:55:00 PM
>
>
> But with two rows of rivets expecting intimate contact over a sizable
> area is legitimate.  Three rows, even more so.
>
> I do agree that the first rivet is much too close to the end of the
> outer tube.  I had one break there, but it was from rough handling.
> Still it should not have broken at that first rivet. The break which
> bisects the rivet hole in the inner tube can easily be seen from a 45
> deg angle to the end of the tube,
>
> As for using self taping screws to hold two tubes. By design, the screw
> must be the major source of conduction, as the threads are close to the
> same in both tubes. Only by tightening the screws enough to deform the
> Aluminum will they pull the pieces together. This approach has
> apparently worked for many, but so has the F12 use of rivets.  When I
> redo the element tips, I will be using more overlap as well as having
> the first rivets at least an inch back from the end of the outer tube
> Whether we like or dislike screws and or rivets, it's evident they both
> work.
>
> With F12, the pop rivets give an additional advantage. "That antenna
> with those elements was pre-assembled at the factory with all element
> joints drilled so the holes will match" If they don't, you have the
> wrong part.
>
> Just don't forget the Penetrox!
>
> 73
>
> Roger  (K8RI)
>
>
> On 3/9/2016 Wednesday 11:25 AM, TexasRF--- via TowerTalk wrote:
> > There are plenty of reasons that this capacitance scenario is bogus. It
> > would be nearly impossible to maintain a spacing of 1 mil or 3 mils 
> between
> > conductors with the pressure created by the element weight and wind 
> forces.
> > Then  there is the ever changing dielectric constant of joint 
> compound as
> > moisture  comes and goes with rain. There is the loss tangent of the 
> dielectric
> > as  well.
> >
> > More likely that a joint like this looks more like a low value 
> resistance.
> > With a few screws or rivets in place even that would be modified to 
> a very
> > low  resistance (negligible).
> >
> > Granted, we have all seen intermittent connections due to corrosion and
> > other causes but invariably they are caused by lack of attention to the
> > proper use of joint compound and/or joining hardware.
> >
> > The concern about stainless steel connecting hardware seems over blown.
> > After all, mobile antennas have been made with stainless steel for many
> > decades  and you never see one that has turned black due to rf heating.
> >
> > Aluminum vs copper conductors also seems over blown. It is very well 
> known
> > that aluminum resistivity is about 28% more than copper. While this at
> > first  sounds like a lot, one can see that 28% more of something 
> that is near
> > zero loss  is still near zero loss.
> >
> > Making low loss connections is another matter though. One can easily 
> make
> > soldered connections with copper; not so much so with aluminum. 
> Perhaps use
> > of  joint compound is advisable in all applications with connections to
> > aluminum.
> >
> > My opinion of course, yours may be different.
> >
> > 73,
> > Gerald K5GW
> >
> >
> >
> >
> >
> >
> >
> > In a message dated 3/9/2016 7:51:01 A.M. Central Standard Time,
> > jimlux at earthlink.net <javascript:return> writes:
> >
> > On  3/8/16 9:09 PM, Bert Almemo wrote:
> >> 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.
> >>
> > Don't forget the capacitance.  9 square inches separated by 1 mil is
> > about 2000 pF
> >
> > at 14 MHz, that's an impedance  of about 5 ohms. Even if there's a 
> bigger
> > gap (say, 3 mils) the impedance  goes up to 15 ohms, and in any case
> > capacitance is lossless: you just make  the element a bit longer to
> > cancel the series  C.
> > _______________________________________________
> >
> >
> >
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> >
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>
> -- 
>
> 73
>
> Roger (K8RI)
>
>
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73

Roger (K8RI)

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