CASE 580G digger starting problem

[<me9]

Yes, it's the same, I would recommend it for all TV aerial leads.

Watcher doing out of the outmollishment?

[Guy King]

The message from contains these words:

Oh, I hang out in the uk.rec.cars.maintenance garage as well.

[Hamish]

Both UHF TV and Sat cable is rated at 75 Ohms, it is just made from better materials a solid core, more tightly braded and a foil wrap. The core insulator is usually a solid plastic. Its is usually slightly smaller diameter to UHF cable. It is also less flexable. Because of the hugh demand for satellite cable it is only about twice the price of UHF cable, but much lower attenuation.

[Duncanwood]

It might be easier to try this

[Weatherlawyer]

I take it the pole is aluminium to save weight when mounted on a roof? More durable than wood and a lot lighter. But the pole is not a part of the signal reciever is it? Can you mount the actual recieving bit directly to a chimney or fashion a more durable anchor?

[Nick]

to avoid having dissimilar metals together in the wet?

[Oz]

Nick writes

Absolutely, particularly in the salty wet.

The only solution is to have the dissimilar metal join in a dry environment. This means it must be potted or sealed.

However note that aluminium has very very poor corrosion resistance under salty conditions, it needs protection.

Hmm....

I would be tempted to see if you cannot rig up a new junction box. IP65 boxes and glands are cheap and will (easily) accept to the diameter of the aly aerial elements. However, having experience of difficult environments (eg milking parlours) you must assume some liquid will gain entry. This means it should still be conformally coated after assembly. That is, both inside the box, and outside round the glands.

[Duncanwood]

Sort of, but aluminium on it's own doesn't like salt spray. & the cables bound t e copper.

[Nick]

I was quite specific about the problem, but many replies address other problems that don't exist in my case. But thanks anyway. The aerial pole is galvanised steel pipe and is in perfect condition.

The rest of the aerial is aluminium tubing, with the active elements connected together electrically with flat aluminium strip, and held by galvanised steel screws. The poor reception is solely caused by the corrosion between the flat strips and the tubing. It is my contention that the steel screws are causing the corrosion, since the rest of the aluminium is in perfect condition.

There are 7 active elements, and thus 14 connections such as in this cross-section diagram (use fixed font to display):

S is a galvanised steel screw A is a flat connector B is another flat connector T is an aluminium tube N is a galvanised steel nut

SSSSS AAAAAAASAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

TTSTT T S T T S T T S T TTSTT BBBBBBBBBBBBBBBBSBBBBBB NNSNN S

The corrosion occurs between A and T, and B and T. All of the flat connectors are connected in series. So there are 28 pairs of surfaces that have to be a good connection. If any one of those is a bad connection then I lose the weakest TV channel. I could probably put A and B together on one side of the tubing and that would halve the number of connections. But that would mean altering the design of the aerial, presumably designed by experts. Yeah right! I'll use anti-corrosive paste for a start. I can easily make aluminium screws and nuts. I could connect a car battery across each joint. That ought to do something!

[Weatherlawyer]

I doubt you will get any joy trying to weld aluminium. But why not try some plastic wrapping on the bolts and ditto gaskets for the washers and nuts?

Talking of gaskets: Have you thought of gasket jointing -Hermatite or something?

[Nick]

There's not much salt really, although the sea is 100 yards away. The rest of the aerial is not corroded. All the connectors are aluminium, and the ends go into a well sealed junction box with the balun, before there is any copper. The only corrosion occurs where the galvanised steel screws are.

[Nick]

I'd need 7 junction boxes for the 7 elements, each with a big hole for the main pipe, two little holes for the element, and 4 flat holes for the connectors. Looks like a nightmare to seal. I'd really rather weld, solder or braze all the joints together.

[Duncanwood]

RS will sell you alloy allen bolts, if M6 fits then any greenhouse supplier can do them cheaply

[Oz]

Hmm....

If I were getting as paranoid as you I would probably be considering buying some hard drawn copper tubing of the same diameter as the aluminium and (using standard solder fittings) converting the aerial to copper instead of aly.

Alternative would be 317 grade stainless (but a tad intractable).

[Stephen Temple]

13CR12 works a bit easier than 304 or 316 stainless, can be welded with a normal stick welder.

[Stephen Temple]

Sorry, should be 3CR12 / 1.4003 stainless. Available from Cromweld.

[Matt]

Use some Duralac as widely used on virtually all properly engineered joints between aluminium and steel

fully assembled spray the whole aerial with conformal coating as previously mentioned.

[Oz]

Stephen Temple writes

Is it Cl- resistant though (like 316)?

[Stephen Temple]

Their website is not responding, but the databook I have says for marine environments, corrosion rate per year (microns/yr) after 2 years is: mild steel 55.9 zinc 2.39 copper 1.45 aluminium .574 to .696 depending on grade

304 stainless .0152 316 stainless .0076 3CR12 (pickled) .194

So not so good as real stainless but cheaper and better than other alternatives

[Hamish]

Given that one can get most if not all of the standard channels on digital sat free with a box costing around 80 pounds for all the bits inc dish and the dish can generally be put discretely in an accesable position, that might be the way to go. Look for it in Lidl next time they are on offer. If you are marginal you are likely to loose it all when all terrestrial digital comes in in any case.