[TowerTalk] F12 C19XR Rivets

[Roger (K8RI) on TT]

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 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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