[Moon-net] Question regarding Loss due to Oxidation

[Edward Cole]

I would be interested in the answer(s), too.

Many years ago I did some waveguide fabrication at work and we used a 
cleaner called Oakite which we preheated the copper then dipped it in 
the liquid.  It came our perfectly bright with a single dip (had to 
wear protective gloves and eye wear).  We rinsed the waveguide after 
dipping and air dried it (fast in the dry desert air).  Then it was 
quite easy to silver solder using a little liquid flux and acetylene 
torch.  The wave guide was 2.15 x 4.30 inches so it took some heat to 
attach flanges.  I expect that the cleaning would last for some time 
if sealed properly.

I did a search on Oakite and this is the name of a company.  They 
have too many products for me to know what we used (back in 
1972).  Might not even be made anymore.  eg. we also used carbon-tet 
for cleaning back then.

My 2.4m dish has about 3m of WR90 to the feed and it has been open to 
air for several years (but covered from rain/snow).  I'm kind of 
worried it has built up some corrosion.  It is a "button hook" or 
"shepard's crook" feed, so not replaceable (mfr long out of business).

73 Ed - KL7UW

At 11:30 PM 3/27/2007, Mark GM4ISM wrote:
>Charlie,
>I am wondering about this too.
>I just built a 6cm EME station and noticed a significant drop in RX
>performance when I added a 2m length of waveguide from the feed to the
>preamp.
>The copper waveguide was a very dull inside, and I wondered about this at
>the time.  I have never noticed any degradation of waveguide professionally
>over many years, but it is not something we go looking for. The fade margins
>are very high on our links and the waveguides are always pressurised with
>dry air. Probably any oxidation is very slow.
>I will be investigating the losses of my section of guide, and let you know
>what I find. As to prevention, I am not sure coating is a good idea, but
>rather a good method of cleaning (chemical etching to restore the surface?)
>may be better.
>Anyone any ideas on this?
>as suggested above, pressurising the guide with dry air is the professional
>long term solution, but I would think it was a little impractical for
>amateur purposes, though if the system is capable of being sealed, it may
>still slow oxidation, especially if a desiccant can be used, (sealed systems
>often breathe a little)
>
>----- Original Message -----
>From: "Charlie Kahwagi" <ibnkarim at bigpond.net.au>
>To: "MOON_NET" <moon-net at list-serv.davidv.net>
>Sent: Wednesday, March 28, 2007 5:08 AM
>Subject: [Moon-net] Question regarding Loss due to Oxidation
>
>
> > Hello all,
> >                can those with experience, advise me how much  loss the
> > oxidation of a copper surface introduces?
> > Is it a problem on uW EME ?
> >
> > I have  noticed heavy tarnishing / oxidation of my 5.7 GHz  and 10 GHz
> > feeds and I am not sure if this is producing any real extra losses into
> > the system.....It doesn't seem to have, from my observations, but I'm not
> > really sure.  My echoes on 5.7Ghz are as weak as they were 6 mths ago!
> >
> > Should I /  or is there a spray or coating I should use on them that will
> > not effect the electrical characteristics,  but will protect against
> > oxidation?
> >
> > Any thoughts, suggestions and observations on this matter would be greatly
> > appreciated.
> >
> > Regards
> > Charlie
> > VK3NX
> > _______________________________________________
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