LNB with moisture behind cover

timo_w2s

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I've got an old white Sharp LNB (which is one of my old favourites before the Black Ultra came along) fixed to a 60cm dish but it's got a few moisture droplets on inside of the plastic feedhorn cover. It's been like that for several years and since the LNB holder had rusted solid I hadn't done anything with it. But the other day the DIY mount feel apart (it was made of wood but lasted 10 years!) so I thought this was a good time to take everything to bits and give the dish a good clean and free up the rusty bits.

The LNB still works but it can't be good for the inside to be constantly damp. I was wondering if I should drill some small holes in the front of the LNB cover to let some air in or would it make the situation worse when it rains? I've tried taking the plastic cover off but it seems pretty firmly fixed down.

Or should I just leave it as it is with moisture inside considering it still works?
 

Lazarus

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The plastic covers can be prised off on some models, but not sure if yours is one of those - I've taken them off using a pair of small screwdrivers blades as levers.

As for the holes, not only will you permit further ingress but might exacerbate the potential for insect nesting.

Leave well alone. Or maybe deploy a hairdryer? Or just tap it gently to encourage the surface tension to break and allow the drops to run off the cover?

PS: If you ever care to dismantle an LNB, the inner casing is hermetically sealed and as indestructible as a dead Hard Disk Drive!
 

timo_w2s

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Thanks. It does look like the cover should come off. I might give it a go tomorrow and see if I can gently prise it off with a screw driver, but it certainly wasn't shifting with just my bare hands.

It's been inside for a week with no sign of the moisture going, and even when there's been some hot summers (remember those?!) with baking sun on the LNB it's still not shifted the drops. The water seems rather well sealed in which is odd since it had to get in there in the first place...
 

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How do you know it's water and not some insect cocoon or waxy discharge?

PS: I added a line to my last Post - the water (if that is what it is) won't harm the LNB innards (although it must potentially degrade the coherence of the signal presented to the dipoles, of course).
 

timo_w2s

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The drops change size and position from time to time. Like now the LNB has been sitting on its side and the drops have moved due to gravity. I'm pretty sure they are water drops. It's a very small mount though.

If I can't get the cover off I'm going to leave it as it is. It's only going to be used for picking up Astra 1 near London so don't need to worry about super sensitivity.
 

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Be careful; the plastic may have become brittle over time.....perhaps warm it gently
 

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Thanks, good point.
 

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Drill a 1mm hole in the side of the plastic cover, stick it in a warm place for a few days then reseal the hole with bathroom sealant?
 

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I wasn't able to prise the cap off with a screw driver and rather than risk damaging the plastic too much I left it.

I like the idea of a small hole and bathroom sealant so I might try that sometime.

But while setting things up in the garden today I realised I'd made a bit of a schoolboy error so I ended up not using the LNB after all.

I was planning on using the Sharp LNB with a Black Ultra on a 60cm dish to get 19E and 23E off the same dish but of course with the dish being so small the LNBs are too close to each other to get a signal from both satellites. However, I'll have a whole load of thin 23mm MultiConnect LNBs spare soon so I might try again and use those later on in the year (along with a home made rain shield to keep the LNBs working in the rain).
 

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If the plastic cover gets damaged, you can always use a cap from any spray can.

I like Analoguesat's method.

One of the effecient moisture absobers is dry rice!
Just take the cover off and put the LNB face down in plastic bag containg rice (from any supermaket).
Keep it sealed for 2 days.
Remove and recap.

It is also used when you drop your mobile phone in water accidently.
:)
 
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