Baffled - Power Down The Wires From An Tv Signal Amplifier

[roy123]

Hi. This is totally baffling, hope someone can help.

In our new house a large tv signal amp is installed and works fine.

It's putting out 20v AC down the coax the tv aerial sockets in the house. TV working fine, good signal etc.

Except.. when I connect the tv aerial tv powered but not on or standby, (5yr old, fairly modern LCD,).

Now the voltage becomes 9v DC (no longer AC) AND - this lights up a 240v mains tester screwdriver.

Voltages measured with a multi-tester, appreciate screwdrivers should be binned or banned - but what's going on!??

Ideas very welcome.

cant edit but to add - voltages measured at out tv aerial socket with tv plugged into another in another room

 

[Marvo]

TV signal amplifiers often have a power supply that puts the coaxial cable at a slight potential. It's not necessarily a fault. I'm not even going to comment about the neon screwdriver and I'm assuming you're using a digital voltmeter. For a more accurate evaluation of the voltage present use an analogue multimeter.

Just out of interest if it's working fine why are you attacking it with you tester and your neon tea-stirrer?

 

[steptoe]

TV signal amplifiers often have a power supply that puts the coaxial cable at a slight potential. It's not necessarily a fault. I'm not even going to comment about the neon screwdriver and I'm assuming you're using a digital voltmeter. For a more accurate evaluation of the voltage present use an analogue multimeter.

Just out of interest if it's working fine why are you attacking it with you tester and your neon tea-stirrer?

:red card

they have their place,

but I do agree, not in the hands of the untrained,

and yes, why are you trying to fix something that isnt broke?  :shakehead

 

[ProDave]

This is all perfectly normal.

Many provide 9V DV to power a sky link magic eye, so when used with a sky box you can watch the sky tv in any room and control the sky box remotely.

I did however once have one tv where this 9V on the aerial lead would power the standby light on the tv, even if the tv was unplugged. Bit it nver actually seemed to bother the tv.

 

[SPECIAL LOCATION]

Hi. This is totally baffling, hope someone can help.

In our new house a large tv signal amp is installed and works fine.

It's putting out 20v AC down the coax the tv aerial sockets in the house. TV working fine, good signal etc.

Except.. when I connect the tv aerial tv powered but not on or standby, (5yr old, fairly modern LCD,).

Now the voltage becomes 9v DC (no longer AC) AND - this lights up a 240v mains tester screwdriver.

Voltages measured with a multi-tester, appreciate screwdrivers should be binned or banned - but what's going on!??

Ideas very welcome.

cant edit but to add - voltages measured at out tv aerial socket with tv plugged into another in another room

Just out of interest if it's working fine why are you attacking it with you tester and your neon tea-stirrer?

and yes, why are you trying to fix something that isnt broke?  :shakehead

The only totally baffling bit I can see is, as has already being pointed out...

What exactly are you trying to do and why??????   :C

From the info given it would appear you are using inappropriate test equipment...

to read something that you don't understand or know where or how you should be testing..

for some reason that is unexplained???

Voltages and signals can be induced into cables accidentally or intentionally dependent upon the purpose of the cable....

TV aerials & their cables by nature are intended to detect electrical signals to convert back into you TV image etc...

Old fashioned TVs had a single cable & aerial going to one TV..

once modern multi-room TV became a need signals had to be boosted and distributed around the home and a single aerial cable cant deliver a sufficient signal to work multiple TV's...

This is where various boosters amplifiers splitters etc. started being fitted...

Some of these devices are powered direct from a plug in PSU..

others are powered down the cable (i.e. a low DC voltage) to a remote amplfier..

e.g. things like masthead amplifiers stuck out on the aerial pole take power from a remote PSU....

UHF tv signals can be sent down the same wire a DC voltage to supply a remote amp/booster... 

but to read accurately what the true signals are, you would need appropriate test equipment and need to know the correct place to test across!

Without knowing the exact kit you have installed its is impossible to say if or what you should be getting at any point on your wiring.... 

So first of all we need to unravel the mystery of

What are you trying to do and why???

Guinness

 

[Sharpend]

Mores to the point how did you discover it in the first place?

 

[SLIPSHOD & SLAPDASH]

I had 240V on a co-ax due to an earth fault on the loft lighting where the amp was plugged in.

 

[Blue Duck]

found 25v ac on some old tails about 250mm from the new ones.....