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@tm.net>;
*To: * <towertalk@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@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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--
73
Roger (K8RI)
---
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