# TV Aerial Cable Broken



## Robell (Mar 13, 2013)

Hi, the built in multimedia unit wouldn't pick up any TV channels last weekend, although the TV in the back of the van picked up perfectly. Had a look at it yesterday and found that the cable from the aerial amplifier to the head unit is broken somewhere (made a cable direct from the amplifier to the head unit to confirm). It was interesting to note that the diameter of the cable from the amplifier was about 2mm, but the one going in to the head unit is about 5mm. I deduce from that there must be a joint somewhere, possibly behind the Sargent unit or on the downward run to the area just behind the driver footwell. Has anybody had to replace / fix this aerial cable and can confirm where this joint is (before I start pulling things apart)? it would make it a lot easier if I knew which area to go to first.

Thanks in advance

Rob


:thumbleft:


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## pippin (Nov 15, 2007)

Can't help you with the problem Rob, but congrats on being able to spell arial, ariel, aeriel correctly!


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## pippin (Nov 15, 2007)

Incidentally, if you do find a break in a co-axial cable do not use a simple twist-the-wires-together as a permanent repair.

It will introduce huge signal losses (due to SWR). 

"F" connectors are probably the easiest way.


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## Pudsey_Bear (Sep 25, 2008)

Standing wave ratio ??, CB days


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## Robell (Mar 13, 2013)

pippin said:


> Incidentally, if you do find a break in a co-axial cable do not use a simple twist-the-wires-together as a permanent repair.
> 
> It will introduce huge signal losses (due to SWR).
> 
> "F" connectors are probably the easiest way.


Thanks Pippin. Never do 'twisted wire repairs' for that very reason. Even on power cables it has t be a proper joint. Seen too many of the 'dodgy' ones on my numerous visits to installations - usually the ones in the far east I hasten to add.

The connectors currently used are the 'F' type, so as you suggest, those will be the ones I use, especially as I have some left over from the satellite cable 'plumbing' in the house. :-$

Rob


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## pippin (Nov 15, 2007)

"Standing wave ratio ??, CB days"

SWR was around a long time before CB was even heard/thought of!

Virtually all consumer TV and video stuff is 75 Ohms whereas virtually all other communications kit is 50 Ohms.

BNC plugs/sockets come in both impedances and there is a surprising mis-match when mixed up.

I just feel in an educating mood at the moment!


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## Pudsey_Bear (Sep 25, 2008)

pippin said:


> "Standing wave ratio ??, CB days"
> 
> SWR was around a long time before CB was even heard/thought of!
> 
> ...


Yes it's been around for a while, I just had a thing about TLAs at the time, I needed to know what the words were even if they meant nothing to me.

Nowadays it's the opposite no one says Kilos or kilograms, its KBs, as they don't know what it stands for, same with MBs, GBs, MLs, we're raising a load of incomplete people.


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## pippin (Nov 15, 2007)

Certainly incomplete (or actually dead) if they don't know:-

"It's mills that kill but volts that jolt"


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## cabby (May 14, 2005)

You just took me back to the 1960's with that.pippin.


cabby


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## Pudsey_Bear (Sep 25, 2008)

pippin said:


> Certainly incomplete (or actually dead) if they don't know:-
> 
> "It's mills that kill but volts that jolt"


Mills ??


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## pippin (Nov 15, 2007)

*Mill*iampères


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## Pudsey_Bear (Sep 25, 2008)

Ah I see, if it'd been MAh I might have got that.


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## pippin (Nov 15, 2007)

Err, no Kev - wrong again.

A lower case m denotes 10-3 = thousandth = milli

An upper case M denotes 10+6 = a million = mega

So mA is milliamps.

And MA is mega amps.

It takes only about 30mA to kill you, if the voltage is much above 55V and especially if it is across the heart.:crying:

I have had shocks of 25kV (thousand) from TV tubes but I survived (obviously!) because there was far too little current available to kill me.

Gives one a hell of a jolt - hence the saying.

The real danger of that is hitting your head on the other side of the room as you recoil violently away!! :surprise:

So, how does one kill you while the other doesn't?

A shock from the 240V mains has all the power of the CEGB behind it. 
It is a very low resistance source which will easily cope with a current draw, limited only by the fuse in your fusebox. 
6A, 32A, 100A or whatever is not going to burn out before you do!:frown2:

The aforementioned TV tube requires only 25 microamps (10-6 or µA which is derived from a high resistance source so the voltage drops right down as soon as you touch it.

Of course most modern consumer units incorporate a RCD or residual current device.

It senses the current going through the live/line wire and compares it to that going through the neutral wire (which in UK is roughly earth).

If that difference exceeds 30mA - which is likely if you touch the live/line then within a specified time of, say, 40ms (milliseconds) then it will trip and save your life.0

But of course you really knew all that - didn't you?:grin2:


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## Pudsey_Bear (Sep 25, 2008)

Never did like electrickery, hence why I ask so many questions about it, then have to ask again because people who know all this stuff think it's obvious, far from it, and us numpties need proper explanations and not numbers or equations to do what we want safely, and get to understand a little bit more. IE my recent microwave on an inverter thread, which is still not clear enough *for me* to proceed, so for now I Google, but leave it alone.


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## pippin (Nov 15, 2007)

No Kev, I don't assume for a minute that it is obvious to you or indeed most people.

Keep on asking questions about things you don't know - that's the way you learn.

Luckily I was taught electrical/electronic theory and have used it all my working life.

I am still learning because a lot of stuff is down to experience - usually of getting things wrong!

Mnemonics like "It's volts that jolts but mills that kills" have a vital place in dangerous situations.

Incidentally, getting back to the microwave/inverter thread.

Knowing the theory would put me off ever trying to run one that way - let alone a hairdryer!!

I know I can be flippant in some of my posts but there is always a good-hearted meaning behind them.


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## Robell (Mar 13, 2013)

Going back to my original posting, I've now had a look into this further and found that the output from the Status Aerial amplifier goes through a small black box and then on to the multimedia unit (whereas the other output from the status amplifier goes directly to the aerial socket at the back of the van).

There's no indication if there's any power to the black box, so after carefully hacking it apart (yes, they ultrasonic weld the lid on  ) I checked the voltage --- which is zero. Now, the two wires (red and black in the second photo) disappear into the loom so heaven only knows where they end up, as the Autotrail wiring information is not detailed enough to show this. 

For now I've bypassed this 'black box amplifier' (using F-type connectors) and everything appears to work fine. So, a few questions to you all :

1) does anybody know which fuse provides the 12V to this 'black box' amplifier? I can't find a blown one in the Sargent unit.
2) is this second amplifier really necessary, as the Status aerial one seems to do the job fine? Was also wondering if this is the reason people say the Status amplifier needs to be turned down sometimes.

Thanks

Rob

ps. the soldered joint on the aerial lead in the first phot is an original, not one I made - I only removed the insulation to be able to make measurements.


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