Vintage c-band question

[turbosat]

Traded out feedhorns on my big dish today since the polarity motor has gotten flaky lately. I took off the lnb and it was coated on the inside with a white powder. The probe itself was shiny and clean, but I couldn't recall seeing this before. I wonder if the gasket between the lnb and the feedhorn body is failing or not tight enough. Or maybe I have a very powerful lnb that is vaporizing the air molecules trapped inside, turning them to dust, lol. Lnb works fine though.

 

[beavs2112]

hi turbosat It sounds like oxidization of the metal inner surface of the feedhorn. My 20 year old Chaparral feedhorn had the same problem. We had similar problems with some brands of two-way radio receivers back in the day. Since there are holes in the front covers of most feedhorns air comes in contact with the metal inner surface of the feedhorn causing oxidization. My solution is to clean off the corrosion then cover the probe with low glue tape and spray the metal with a thin coat of clear lacquer. Remove the tape off the probe and ya should be back in business.

 

[DK_Sat]

I had oxidization problems with my Chaparral II plus c-ku feedhorn i had no LNB cover on it , i spray some white vinegar in the feedhorne and clean with a rag.
On my other dish i did not get any oxidization i had i LNB cover on it both Dishes are over 21 years old

 

[turbosat]

This lnb is probably 5yrs old, so its not that old. The little rubber gasket looked very flat when I took it apart, so I don't think it was doing a good job of sealing. I did manage to find a new one, glad I never throw anything away, lol.

 

[Anole]

sounds familiar

Just recently (6 months ago?) I think it was TruckRacer who started a similar thread.
He was complaining about the white powder on his Chaparral Orthomode feedhorn.
I have a similar condition, with the white chalky junk migrating under some of the paint, causing it to flake off.
Not satisfied myself with any of the answers I've seen, so I'm still keeping an open mind.

 

[Cadsulfide]

Not too much to be done about pot metal corrosion, cleaning it off every few years seems to be a workable solution.Try scotchbrite

 

[Anole]

Chaparral claims it's cast aluminum construction.
So, there must be some good solutions to aluminum corrosion...

 

[turbosat]

Anole that sounds as good as any explanation I've heard. So I think the logical solution is a better gasket around the mating surfaces to keep out the air. I remember putting silicone completely around the edges of an old lnb years ago, thinking the little rubber gasket maybe wasn't enough, perhaps that wasn't overkill after all, lol.

 

[Magic Static]

Would it be possible to seal a little dessicant bag inside to eat up the oxygen and prevent oxidation?

 

[cracklincrotch]

Paint will not adhere to aluminum well. When I got my most recent BUD I was going to paint it as a lot of the paint flaking off the aluminum mesh. After doing some research on painting aluminum I'd found that aluminum really needs to be etched with an acid, rinsed thoroughly and painted ASAP as the aluminum will begin to oxidize rapidly. I misted my mesh with some hydrochloric acid, rinsed with a garden hose, and sprayed it a latex paint that was compatible with aluminum.

A little bag of silica gel won't work as all it does is absorb moisture. That's not was causes the oxidation. Exposure to the air is enough. If the blisters are sanded, etched (even vinegar will work), rinsed, and hit with some decent primer/paint, you should be good to go.