TV aerial water ingress

[JohnD]

how did the water get into the junction box then?

a drip loop will also (mostly) stop water running down the cable

 

[DIYspanner]

ref: How did the water get into the box?


My thoughts are that the junction box has what I assumed to be a a drain hole when I installed the aerial, in the bottom of the box.

I suppose that in damp conditions, moisture enters the box through this hole.

Perhaps if I were to seal the hole and run a new cable?

 

[Sam Gangee]

What I be right in thinking aerials with F connectors and a plastic protective over gland are a better type of aerial than those like mine where the cable passes through a grommet into the termination box ?

"Better" in what way? I've seen F connector aerials that were complete rubbish. Log-periodic aerials are the most versatile and robust in my experience. They also have an almost linear gain spread and better side and rear rejection than "Yagi" types. Many professional installers have switched to log-p aerials.

 

[Lucid]

ref: drip loop.

I've been to plenty of existing aerial installs where the aerial is the type with a cable junction box. A drip loop wouldn't have helped in any of them because the junction box is at the high point (i.e. it's fixed to the boom of the aerial an acting as the cable junction point). Using drip loops where water is running down a cable though is still good practise.

What I've regularly found is that the junction box lids have popped open. I suspect this is down to weathering; mostly freeze/thaw and the plastic going brittle after years of UV exposure. On more than a few occasions I've seen that the cable boot wasn't fitted or may have been poorly installed. This just makes it easier for water and weathering to do their worst.

If I'm called in to do remedial work on such installs then I now tape the boxes closed with self-amalgamating tape. This stays reasonably flexible despite UV and frost exposure. This is better than standard electricians tape which goes hard and brittle. I still think it's a false economy to reuse these budget aerials after going to the trouble of replacing the cable damage they caused, but some customers have a rather short term view. Anyway, the point is to seal the lids and block any water ingress points if possible.

 

[DIYspanner]

Very interesting reading folks, most obliged.

Is there any advantage to outside aerials compared to those mounted in a loft ?

Since I live in a valley, there's a big hill between the TV transmitter and the aerial anyway so a few tiles on the roof probably wouldn't make any difference if I move the aerial into the loft to avoid the rain ?

My comment on F connectors being better was just my opinion - if I'm mistaken, fair enough, thanks for the informed feedback.

 

[Sam Gangee]

F plugs are better than TV plugs (which were originally designed for medium wave radio) and generally better than screw or clip connections for impedance-matching.

However, aerials incorporating F connections are not necessarily better performers overall, or more robust, than aerials which have inferior connections.

Since you live in a valley where the signal is weak, every dB counts. You'll lose at least 3dB (50%) by installing the aerial in a loft so the question is .. do you feel lucky?

Of course there's no harm in testing the aerial in various locations and choosing the one that provides the most reliable viewing. In fact that's the logical thing to do - just don't finalise your plans until you've done the tests.

 

[DIYspanner]

Are these a good investment for signal tuning?


http://www.ebay.co.uk/itm/PRO-TV-SA...?pt=UK_Sound_Vision_Other&hash=item3a8b46fda1

 

[Sam Gangee]

I think you mean "signal measurement"?
In my experience, the cheap ones aren't terribly helpful in weak signal areas. A compass is even cheaper and more useful. Check signal with a Freeview TV.

 

[DIYspanner]

So for signal measurement, my existing method of using google maps to find the angle between the TV transmitter and the aerial is crude but adequate ?

 

[Sam Gangee]

Normally a compass is fine - get the bearing from the Wolfbane site - but it occurs to me that you are in a valley. Therefore the strongest signal might be coming from an unexpected direction. In that case a good signal meter might be needed.

 

[DIYspanner]

ref: where the signal is weak, every dB counts

So weaker signals give a weaker dB value?

Do this mean the more elements on the aerial the better?

 

[Sam Gangee]

ref: where the signal is weak, every dB counts

So weaker signals give a weaker dB value?

Do this mean the more elements on the aerial the better?

Generally, yes. But beware! I've seen eBay adverts where the number of elements AND the gain were grossly exaggerated. Gain should always be expressed in dBd (not dB or dBi) and WITHOUT adding any gain from a built-in amplifier. In addition, the gain quoted is always the maximum at a specific frequency. So, for example, a Yagi aerial quoted as having a 12dBd gain may only have a 6dBd gain at the extremes of the UHF band.

In contrast, a log-periodic aerial has an almost flat gain curve so one quoted as having a 10.5dBd gain may only drop 0.5dBd at the extremes. In addition, a log-p has better rejection characteristics. This means that it picks up less signal to its sides and rear. So the overall performance of, say, a 9dBd log-p is often better than that of a 14dBd Yagi.

 

[DIYspanner]

Thanks for your expert advice Sam


When it dries up I'm going to take the aerial I have down, re-cable it then seal the junction box with some gutter sealant I've bought.


The aerial's been in situ for about a year and from the ground I can't see any damage from the weather or birds.

Only thing is its on a 1.5m pole and tends to sway in high winds but I only get spluttery picture and sound when its raining heavy.

 

[Sam Gangee]

I'm a great believer in recycling and "if it ain't broke..".
If the aerial is mechanically sound and you can make a good, reliable connection, why waste money on a new one?

 

[DIYspanner]

One thing about spluttery picture and sound, it makes ski jumpers look like they're jumping a hell of a long way.