[TowerTalk] Silver Epoxy for Antenna Work?

[K8RI on Tower talk]

Joining aluminum with solder or welding is an art and a difficult one at 
that. "Brazing" is a term referring specifically to a group of alloys.  It 
also introduces stresses that sooner or later will cause cracking and 
eventual failure.
Although Aluminum can be weldied using an OxyAcetylene torch which is much 
easier than propane, it is still easier to us a TIG welder.


> In the past, I have used aluminum "welds" (actually brazes, using a 
> propane
> torch system) to attach capacity hat rods to aluminum tubing for my 40 
> meter
> yagi.  The brazes are cracking, resulting in loose joints that arc.  I 
> need
> to come up with another plan.
>
> One option is to use silver bearing epoxy to attach the rods to pieces of

I have used silver epoxies and low temperature silver solders, but never on 
Aluminum. Most epoxies are subject to deteoriation from weathering and in 
particularly, UV light.  Typically they also require using a fillett to 
support the actual joint.

Were it me, and it's not, I'd fashion some brackets and rivett the rods, at 
the top and bottom at the end of the element, then if necessary, use epoxy 
to fill the joint to prevent movement and reduce movement. (Don't trap water 
though) The rivetts would give both a good electrical and mechanical joint. 
However rivetts are also subject to flexing, cracking, and corrosion. So you 
might gain a bit by adding epoxy, however the antenna manufacturers do not 
resort to that, or at least I've not seen any.

Solid rivetts are strong and sturdy, but require a good technique and 
bucking bar to install.  Length to diameter ratios are also important. 
Remember they've been holding some mighty big and fast airplanes together 
using rivetts for many decades. Mine is 47 years old, cruises at almost 200 
MPH,  and the rivetts are still good.

Pop rivetts are easier to use, but more flimsy and fail much sooner than 
solid.  In between are the "cherry max" rivetts and they are structural 
while the standard pop rivett is not considered so.

> aluminum angle, then use rivets to attach the angle to the elements.  This
> epoxy is conductive, and appears to have been developed to allow repairs 
> to
> be made on PC boards.
>
> Has anyone used silver bearing epoxy at RF before?  My concern is that
> either the current carrying capacity isn't sufficient, or that it is lossy
> at RF.
>

My main concern with the silver bearing epoxy would be how it lasts out in 
the environment.  My experiences indicate it would likely be relatively 
short lived, but "they" may have come up with better materials since I 
worked in the semiconductor industry.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
> Thanks for any input in advance.  Comments of the form "why don't you use
> attachment method X" are welcome, but I really need an answer to the
> question "will silver epoxy work?"
>
> ***dan, K6IF
>
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