TV aerial corrosion

I have a problem with corrosion on my TV aerial.
It's made mostly from aluminium but is held together with 3/16 inch
galvanised steel screws, as are all the aerials that I see anywhere.
There are 11 round elements, 6 of which are electrically connected
alternately together by flat pieces of aluminium giving a total of 24
pieces of aluminium that touch each other, clamped together by the
screws.
About every six months TV reception gets bad, and I fix this by taking
the aerial apart, sanding the surfaces and putting petroleum jelly on
them. I used to use CRC but that lasted only a month.
It's really difficult to do this because the aerial is 10 metres up on
a roof with a 60 degree slope. TV reception is really bad here so I
need a large outdoor aerial as high as possible.
I have tried to get aluminium screws but without success. They would
probably be too weak anyway.
I imagine that stainless steel screws would still cause a problem.
I have considered taking it somewhere to weld the connections together
but it's about 2 metres square and fragile and rather hard to
transport.
Any brilliant ideas?
Reply to
Jack
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How about aluminum pop rivets? That should get around the galvanic corrosion, at least. But if you ever need to take it apart again, you will not have a pleasant job ahead of you.
How about getting a spare antenna, and mounting them on a pole which is hinged at about half way between antenna and roof -- with an extension of the pole from the antenna continuing down to near roof height so you can tip the antenna to the side, unbolt it and send it down by rope, haul up the other, connect and swing back up, and take your time on the ground fixing the previous antenna.
Good Luck, DoN.
Reply to
DoN. Nichols
(1) Pop rivets.
(2) When you re attach everything next time coat each junction with epoxy. When this cures, give the whole aerial a coat of paint.
(3) Rig a hinged mast so you need only turn a crank to lower the aerial to the ground rather than screwing with continually climbing on the roof. (Sooner or later even sober roofers fall off roofs.)
Reply to
Roger Shoaf
Try a product called CRC Soft Seal.
It's produces a soft, flexible coating that is extremely weather resistant and water-proof. We used to use this liberally when I was doing commercial VHF/UHF antenna installations. I seldom (if ever) had to go back to an antenna due to corrosion problems.
Once you've bolted everything back together *then* spray all the electrical contact areas and any place where you're likely to get galvanic corrosion (ie: where any dissimilar metals are in contact)
Use two coats if you really want long-term protection.
-- you can contact me via
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a cruise missile?
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Reply to
Bruce Simpson
You could try that black anti-corrosion cream that electricians use on aluminum joints. Sorry, can't think of the name right now.
Vaughn
Reply to
Vaughn
We used DC-4 from dow corning on the antenna on top of an aircraft carrier. that was a harsh environment.
the stuff is a bit expensive.
Reply to
Charles
It just occurred to me that I could make some aluminium screws, say 1/4 inch diameter. Does anyone know if I can use standard taps and dies on aluminium?
Reply to
Jack
Have you tried using an aerial in the loft? The signal is weaker but so is the weather.
John
Reply to
John Manders
There is no loft. The ceiling has aluminium foil on top of the plasterboard which is 6 inches away from the roof which is sheathed in corrugated iron. I guess that not much of a signal will get through that :) Besides the aerial has to be much higher than the house because there is a hill between the house and the TV transmitter aerial.
Reply to
Jack
why not replace the steel rivets with alum. rivets.... then you will not have this problem?????
Reply to
dbird
On Wed, 07 Jul 2004 05:25:47 GMT, snipped-for-privacy@nospam.thanks (Jack) vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
This is almnost a rec.boats.building question.
I also live in the frignes of TV reception, and have seen corrosion between steel fasteners and alum aerials.
The aluminioum antenna presumably needs aluminium to aluminium contact. Pet jelly is bad there. Steel is bad to hold it together.
Stainless will cause a lot less problems than galv/zinc steel. There may still be trouble. But less.
Dissimilar metals in contact in a hostile environment = trouble.
You need to maximise the aluminioum contact that is needed to make the aerial work (elements) but minimise the contact to other metals. Coat all screws with silicone, unless that screw is the contact between elements. make sure all contact between elements is well-covered with Wd-40 or whatever. If the screw _is_ the contact, then use stainless or an alum rivet. Seal the joint (silicone again).
Reply to
Old Nick
Change antenna brands? I've never seen the construction you describe, the Yagis I've put up have all been constructed so the elements pivot so they can be folded to fit in a quite narrow and long square box. The pivots are aluminum rivets, the connecting cross-over links are aluminum rods that are also riveted, usually they're designed so that the element insulators(molded plastic) are above the fasteners to provide some weather protection, the insulators also have stamped aluminum detent bars fastened so that the element snaps into them when it's pivoted out. The only threaded connectors are at the terminal block, central beam splice bolt(if there is one) and the masthead clamp, very few tools needed to assemble one, just haul it up to the roof and start pivoting the elements out. I've replaced 2 in the last 30 years on my parents' house, both because of windstorms, not because of bad signal quality. Maybe there's not enough demand in NZ for the kind of outside antennas we can get here in the US. They're usually US$50-80 for the sort that you can get at Radio Shack.
Another popular option in the last few years has been the outside amplified antenna. I've got one of these myself, I can pick up a station that's at least 60 miles away over a range of high hills, the antenna sits about 15' off the ground. Looks like a two foot diameter flying saucer, there's other configurations. You do have to pass current up the coax to power the internal amp, though. It's a completely sealed unit.
My past practice has been to use silicone grease over connections and to use silicone rubber boots and grease over the coax connections. Might be silicone RTV would be something to dab over your screwed connections, certainly wouldn't hurt. Might be you could rig some sort of overhead covering for those connections, too, at least keep the direct rain off. Glass-reinforced plastic is what's usually used here.
Stan
Reply to
Stan Schaefer
You may want to use one of the conductive greases made for the purpose.
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Kevin Gallimore
Reply to
axolotl
Good suggestions you have already received about placing the antenna on a "let down" pole - even if you need to use a pulley/rope combination to lower the antenna/pole to the ground. As far as corrosion, I would look for a product called Noalox used by electricians to place aluminum connections on busbars, etc. Your friendly electrical supply outlet should be able to help you there. It conducts electricity but eliminates corrosion. That may work for you if you don't overdo the application to the connections. HTH Ken.
Reply to
Ken Sterling
Not a brillant idea, but microcrystaline wax and mineral oil is likely to last longer than petroleum jelly. Microcrystaline wax is the dark brown stuff used by lost wax casting folks. It is the same as the wax in cosmolene ( at least I think so ) but cosmolene has more mineral oil mixed with it so it is softer.
Regular taps and dies work on aluminum.
Dan
snipped-for-privacy@nospam.thanks (Jack) wrote in message
Reply to
Dan Caster
Pop-rivet ? can that work?
Tig Weld ?
Martin
Reply to
Martin H. Eastburn
Yes -- but you will probably want a good hard aluminum, like 6061-T6. Soft aluminum would be a likely to twist off in a die as to thread cleanly.
Use something like kerosene or WD-40 for cutting lubricant to minimize gumming of the taps and dies.
Good Luck, DoN.
Reply to
DoN. Nichols
Thanks, I'll try that as it's probably available in this country. First I'll have a go at making some aluminium bolts. I'd like to be able to take the aerial apart in future if necessary, and I'd rather not use an angle grinder while clinging to a 60 degree roof.
Reply to
Jack
I've already tried a rotatable and retractable mast. This tended to shift and be damaged in strong winds. Besides a 10 metre (33 foot) mast is a major exercise for me to lower and raise. I tried having the mast at the top of a 70 foot tree but it was such a pain to climb it to turn the aerial around. Besides, the rats liked chewing the coax lead.
I'll have a look next week to see what is available. Thanks everyone for all the suggestions.
Reply to
Jack
A guy near me once had an aerial mast that hinged about 8 feet off the ground, between two uprights, on a pivot pin. There was on old water tank attached to the hinged part. It hung below the pivot point like a pendalum (sp) Whenever he had to work on the unit, he pulled a locking pin out and drained water from the tank with a valve. The aerial mast would slowly lean to the ground. When he was through, he attached a garden hose to the tank valve and refilled it with water. The mast would stand back up slowly and steadily under full control. I would assume he used some sort of anti-freeze solution in it, but then again, he was a drunk, so who knows..
RJ
Reply to
Backlash

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