CASE 580G digger starting problem

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

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.

It might be easier to try this

Yes that's a good idea which I will try. But wouldn't it be good to avoid having dissimilar metals together in the wet?

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.

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

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.

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.

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

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).

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

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

Stephen Temple writes

Is it Cl- resistant though (like 316)?

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

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

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.

Can you explain a bit more please, does that apply to weak Sky signals on Astra 2D - eek!

CASE 580G digger with the starting problem is fixed by the way, thanks for all the original replies and suggestions.

-- Holly, in France Gite to let in Dordogne, now with pool.

Hi,

Try painting the joints with a few coats of zinc rich primer; zinc is used to protect aluminium hulls and fittings in seawater so should protect the aluminium. In any case it will create another conductive path between the joints.

cheers, Pete.

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Terrestrial digital is being transmitted on low power at the moment so as not to interfere with the existing analogue channels. When the analogue channels are switched off the digital channels will be transmitted at increased power. This means that digital coverage will be greatly improved.