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TV Coaxial sockets

David Schweizer

By David Schweizer
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David Schweizer Veteran II

David Schweizer

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I am about to fit a couple of TV Coaxial sockets on the boat and have noticed that some seem to have a small resistor in the signal line, whilst others are wired direct. Does anyone know what the function of the resistor is, and as some sockets do not have one how important is it?

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I am about to fit a couple of TV Coaxial sockets on the boat and have noticed that some seem to have a small resistor in the signal line, whilst others are wired direct. Does anyone know what the function of the resistor is, and as some sockets do not have one how important is it?

 

Possibly to attenuate the signal if being used in a very strong signal area?? :unsure:

 

I've fitted loads of these over the years at home and in caravans and TBH I've never encountered one with a resistor in and never noticed any adverse affects by fitting one without.

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bizzard Veteran II

bizzard

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Posted (edited)

It might be an inductor - to act as some sort of interference filter... some look like resistors

 

Nick

It might even have a seducer which would try to lure you to plug a plug into it.

 

Ps Most sockets being of the female type like.

Edited by bizzard
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David Schweizer Veteran II

David Schweizer

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Posted (edited)

Right you are. A Sinductor then.

Why do you seem to be determined to derail this thread Bizzard? Has no one told you that repeating the same old joke does not make it any funnier?

Edited by David Schweizer
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by'eck Veteran

by'eck

Posted
Posted

I am about to fit a couple of TV Coaxial sockets on the boat and have noticed that some seem to have a small resistor in the signal line, whilst others are wired direct. Does anyone know what the function of the resistor is, and as some sockets do not have one how important is it?

 

Splitters have resistors in to maintain the correct 75Ω impedance match to connected devices and so that one device doesn't affect the other.

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Arthur Brown Influencer

Arthur Brown

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Posted

The aerial downlead is a transmission line, and signal arriving at a cut end is reflected back along the line. If you have one aerial feeding one socket it matters not, but if you have one aerial feeding several sockets by T junctions the reflected wave will re-enter the aerial cable and arrive at other sockets at a different time from the direct signal. This will impair the TV performance and may give ghosting effects, or may just make finding the right station harder. Other failure modes will happen in the digital domain.

 

The resistor absorbs the energy that would have been reflected.

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alan_fincher Veteran II

alan_fincher

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The aerial downlead is a transmission line, and signal arriving at a cut end is reflected back along the line. If you have one aerial feeding one socket it matters not, but if you have one aerial feeding several sockets by T junctions the reflected wave will re-enter the aerial cable and arrive at other sockets at a different time from the direct signal. This will impair the TV performance and may give ghosting effects, or may just make finding the right station harder. Other failure modes will happen in the digital domain.

 

The resistor absorbs the energy that would have been reflected.

I haven't read the other obvious (just from the thread title) April 1st threads, but this single post certainly rates as "nice try" ! :rolleyes:

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Semitrad Collaborator

Semitrad

Posted
Posted

I am about to fit a couple of TV Coaxial sockets on the boat and have noticed that some seem to have a small resistor in the signal line, whilst others are wired direct. Does anyone know what the function of the resistor is, and as some sockets do not have one how important is it?

 

These resistors can be used as a DC block, where a masthead amplifier is used and the main cable carries the 12V supply.

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Nickhlx Veteran

Nickhlx

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Posted (edited)

These resistors can be used as a DC block, where a masthead amplifier is used and the main cable carries the 12V supply.

 

I thought (know) it is capacitors that are able to DC block - resistors just resist DC flow ( and absorb reflection energy)

 

Nick

Edited by Nickhlx
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smileypete Veteran II

smileypete

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Posted

I am about to fit a couple of TV Coaxial sockets on the boat and have noticed that some seem to have a small resistor in the signal line, whilst others are wired direct. Does anyone know what the function of the resistor is, and as some sockets do not have one how important is it?

Sure it's a resistor? Why not put a meter on it.

 

cheers,

Pete.

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Keeping Up Veteran II

Keeping UpDonate to Canal World

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Can you tell the value of the resistor (may be printed on; or if it's got bands of coloured paint showing the value, what are the colours?)

 

The only use I can guess at is possible protection against short-circuit in a system that is fed with 12v dc for an amplifier.

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David Schweizer Veteran II

David Schweizer

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Can you tell the value of the resistor (may be printed on; or if it's got bands of coloured paint showing the value, what are the colours?)

 

The only use I can guess at is possible protection against short-circuit in a system that is fed with 12v dc for an amplifier.

The there are three resistors in the socket I am looking at, one each from each input and joined together at the output end which is joined to another one which is connected to the socket centre, They are all the same value - colours red, purple, black, silver. If my memory serves me correctltly that makes them all all 27ohms with a 10% tolerance.

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Nickhlx Veteran

Nickhlx

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Posted (edited)

The there are three resistors in the socket I am looking at, one each from each input and joined together at the output end which is joined to another one which is connected to the socket centre, They are all the same value - colours red, purple, black, silver. If my memory serves me correctltly that makes them all all 27ohms with a 10% tolerance.

 

(rough) Impedance preserving ?

 

Nick

Edited by Nickhlx
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Guest

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Posted

Can you tell the value of the resistor (may be printed on; or if it's got bands of coloured paint showing the value, what are the colours?)

 

The only use I can guess at is possible protection against short-circuit in a system that is fed with 12v dc for an amplifier.

 

Aren't they normally in the splitter box though not the co-ax socket??

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by'eck Veteran

by'eck

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The there are three resistors in the socket I am looking at, one each from each input and joined together at the output end which is joined to another one which is connected to the socket centre, They are all the same value - colours red, purple, black, silver. If my memory serves me correctltly that makes them all all 27ohms with a 10% tolerance.

 

That confirms it is definitely a two way splitter as per post #9. The three nominally 25Ω resistors (27Ω is nearest common value) should be in a star configuration. This will maintain the correct 75Ω impedance to match each connected device as well as isolating each to prevent reflected signals. It will give around 6dB loss though leaving you with ¼ of the signal.

 

An alternative to this passive device is an active amplifier/splitter. More info here.

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jelunga Influencer

jelunga

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Possibly to attenuate the signal if being used in a very strong signal area?? :unsure:

 

I've fitted loads of these over the years at home and in caravans and TBH I've never encountered one with a resistor in and never noticed any adverse affects by fitting one without.

 

 

I thought resistors would not work as resistors on AC circuits, and a ~TV signal is certainly AC. More likely it is to reduce interference from other ellectical devices

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Semitrad Collaborator

Semitrad

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The there are three resistors in the socket I am looking at, one each from each input and joined together at the output end which is joined to another one which is connected to the socket centre, They are all the same value - colours red, purple, black, silver. If my memory serves me correctltly that makes them all all 27ohms with a 10% tolerance.

 

That sounds more like a splitter unit than a simple socket!

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