TV Signal

In article , DerbyBorn writes

The screen isn't earthed very well? Check the connection inside the faceplate.

Would you expect the faceplate to be earthed? The ones in my old house weren't. I found this to my cost when I unplugged the aerial cable from the DVB-T capture device in my PC, while holding the metal aerial plug in one hand and the earthed metal case of the PC in the other. There was a definite tingle - strong enough to think "ouch, that hurt - I don't want to do that again". It turned out that my TV (connected to another arm of the aerial cable) had about 200 V between the screen of the aerial (and of audio phono sockets) and mains earth, although with a very high resistance in series. By simulating my body resistance with resistors (I really didn't want to get another shock - it was that strong) I established that the voltage that my body had experienced was about 90 V (potential divider of about a megohm internal resistor in TV and about 300 kilohm human body resistance).

I'd check the lead and plug/socket. I'm afraid most people don't seem to have the knack of fitting Belling Lee style connectors to coax and a poor braid connection is all too common.

It is possible there is a bad joint inside the TV but I'd check the connector first.

In article , NY writes

There will be a clip of some sort to which the braid of the aerial cable should be attached. Also the OP should check carefully for any stray strands of braid which may be coming into contact with the central core when the cable is flexed. The symptoms smell of earth problems.

bert wrote on 04/07/2017 :

No, you can expect a tingle from the coax screening - it is absolutely normal and due to the capacitive coupling. It should not be grounded.

Capacitive coupling (in the receiver) was only necessary when TV receivers were all AC/DC with the one side of the mains connected to the chassis (and many sets had reversible two pin connectors on the back so it was a 50-50 chance whether the chasis was live or not.

What if there is a masthead amplifier - are you just going to let it float and pray that the whole system never gets connected to the live mains because of a fault?

What if it connects to a distribution system feeding two or more outputs so that a fault on the equipment connected to one output could render all the other outlets live?

In article , Terry Casey scribeth thus

No not rubbish, it does not -need- to be grounded and never has.

Back in the day that was the case but we never connected the aerial lead to earth never seen it done. These days with some type of switch mode power device there may well be some leakage but in effect no different to what's been around for years and still no problem.

So how do and do all those masthead amps survive, what is the fault condition that will render them damaged?

Distribution systems as Bill Wright will tell you have each and every outlet connected to an Earthing bar just in case some pillock does bypass the isolator in the TV and feed mains up their co-ax distribution cable!.

It is worth noting that in general it does no partcular harm to earth an aerial and that the 'tingle' you may get from a TV chassis - of which the only accessible bit is the coax socket outer - is usually due to the RFI suppression and lack of mains earth. In short there will be capacitors between live and chassis and neutral and chassis on a two wire system. leaving the TV frame at 110V though with a pretty high impedance.

In the case of a laptop computer, not high enough to prevent it destroying a serial port on another machine to which it was connected.

I would definitely earth any two wire TV system that shows this sort of behaviour.

It can blow electronics to which it is connected otherwise.

Though normally any piece of kit that is earthed, will ground theTV as well.

Reread what you are replying to. The OP said it should not be grounded full stop. This implies never, which is not true.

I did not say it should always be grounded. In fact I think it unlikely that any aerial feeding one set only would ever be grounded

If it was a single feed there would normally need to be an earth connection as I said but there are circumstances where it is not only desirable but esential

Double isolated PSUs these days are very good but that has not always been the case.

What Bill says reinforces my comments. A pillock induced fault is still a fault, whether you like it or not

The the US TV aerials always have a ground wire.

Bill

Yes - they suffer from w_tom remember him;?..

He was the guy who wanted to attract lightning to private dwellings wasn't he?

Bill

In article , Terry Casey scribeth thus

Well in years mispent in the TV trade never once saw it done!.

So how would they be damaged then?.

LOL!

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