I meant to reply to this query earlier,  but got sidetracked.  What I was going 
to suggest was that you look at the interfaces between stainless steel and 
aluminum.  They are potentially problematic, because SS and aluminum have very 
different galvanic potentials, and “in the presence of an electrolyte” create a 
battery with a significant corrosion-causing voltage.  This will cause serious 
galvanic corrosion of the aluminum.

More specifically, the aluminum alloys most often used for antennas have a 
galvanic potential of -0.8 volt to -1.0 volt.  Depending on the stainless steel 
alloy employed, it can have a galvanic potential of about -0.05 volt to -0.25 
volt, which means a voltage differential of anywhere from 0.6 volt to 1.0 volt. 
If there is moisture in the air (which means most places in the world), it will 
create an electrolyte, and corrosion will commence. 

I have always been amazed that the standard practice in antenna building, both 
commercial and home brew, has been to use aluminum tubing and stainless steel 
fittings. That is, in my mind,  a recipe for disaster.

How to eliminate galvanic corrosion?  

1. Use aluminum bolts, nuts and fittings with aluminum tubing.
2. Use cadmium-plated or zinc-coated fittings with aluminum tubing.
3. Use stainless steel fittings with stainless steel tubing.
4. Use brass or copper fittings with brass or copper tubing
5. Use soldered copper joints.
6. Protect interfaces between dissimilar metals so that no moisture can ever 
get into the metal joint. 

There are other approaches that provide low galvanic potential difference, but 
the above are tested and useful.

Lew N6LEW


> On Jan 14, 2016, at 9:39 AM, Vic Rosenthal 4X6GP/K2VCO <[email protected]> 
> wrote:
> 
> I would like to thank the numerous hams who responded to my plea for help.
> 
> The problem that was causing my SWR to rise with high power was not in my 
> shack. The tuner, balun, coax and open wire line were all 100%. The trouble 
> was at the connection of the feedline to the antenna.
> 
> The connection was made where stainless steel bolts passed through the 
> tubing. The bolts heated up rapidly when running over 500w. At first I 
> thought the connection was poor, but improving it did not help. From the way 
> it was heating (away from the point of contact of the lugs to the antenna 
> tubing) I think that it was due to the ferrous material (stainless steel) of 
> the bolts heating due to eddy currents in the strong RF field.
> 
> I have experienced this phenomenon in amplifiers, but never an antenna!
> 
> I will change the method of connecting the line on Sunday and I hope it will 
> solve the problem.
> -- 
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[email protected]
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [email protected]
> 

Lew Phelps N6LEW
Pasadena, CA DM04wd
Elecraft K3-10 / KXV144 / XV432
Yaesu FT-7800 
[email protected]
www.n6lew.us

Generalized Law of Entropy: Sooner or later, everything that has been put 
together will fall apart.





______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]

Reply via email to