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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

Aerial input.



 
 
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  #1  
Old December 28th 13, 01:33 PM posted to uk.tech.digital-tv
Dave Plowman (News)
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Posts: 5,342
Default Aerial input.

What would you expect to measure across the UHF aerial input on a modern
TV, resistance wise? It is working ok - but making the short circuit light
come on on the aerial DA. It does indeed read short circuit. The Topfield
PVR reads approx 175 ohms, and having that before the TV seems to work
fine. But I'm wanting to move things around so this won't be possible.

--
*Am I ambivalent? Well, yes and no.

Dave Plowman London SW
To e-mail, change noise into sound.
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  #2  
Old December 28th 13, 02:51 PM posted to uk.tech.digital-tv
Ian Jackson[_2_]
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Posts: 2,968
Default Aerial input.

In message , "Dave Plowman (News)"
writes
What would you expect to measure across the UHF aerial input on a modern
TV, resistance wise? It is working ok - but making the short circuit light
come on on the aerial DA. It does indeed read short circuit. The Topfield
PVR reads approx 175 ohms, and having that before the TV seems to work
fine. But I'm wanting to move things around so this won't be possible.

I'm surprised that the inner-to-outer reads a low DC resistance. As you
have found, this may compromise the working of any equipment connected
to it. I would expect it to DC blocked - probably with a high-resistance
static discharge leak. On the other hand, does the TV set aerial input
have the option of providing line power (5 or 12V)? Maybe that is
complicating things.
--
Ian
  #3  
Old December 28th 13, 03:02 PM posted to uk.tech.digital-tv
Dave Plowman (News)
external usenet poster
 
Posts: 5,342
Default Aerial input.

In article ,
Ian Jackson wrote:
In message , "Dave Plowman (News)"
writes
What would you expect to measure across the UHF aerial input on a
modern TV, resistance wise? It is working ok - but making the short
circuit light come on on the aerial DA. It does indeed read short
circuit. The Topfield PVR reads approx 175 ohms, and having that before
the TV seems to work fine. But I'm wanting to move things around so
this won't be possible.

I'm surprised that the inner-to-outer reads a low DC resistance. As you
have found, this may compromise the working of any equipment connected
to it. I would expect it to DC blocked - probably with a high-resistance
static discharge leak. On the other hand, does the TV set aerial input
have the option of providing line power (5 or 12V)? Maybe that is
complicating things.


I've just checked a Humax PVR and that is the same - a dead short to DC.
So perhaps a transformer of some sort on the input?

This all came about because I happened to be where the DA is and saw the
red 'short' light on - but it does still seem to work ok like that. But is
definitely the TV causing it as it goes out if I unplug it - but leave the
circuit to it from the DA plugged in. Including the fly lead from wall
plate to TV.

--
*Do infants enjoy infancy as much as adults enjoy adultery? *

Dave Plowman London SW
To e-mail, change noise into sound.
  #4  
Old December 28th 13, 07:35 PM posted to uk.tech.digital-tv
Woody[_5_]
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Posts: 1,865
Default Aerial input.

"Dave Plowman (News)" wrote in
message ...
In article ,
Ian Jackson
wrote:
In message , "Dave
Plowman (News)"
writes
What would you expect to measure across the UHF aerial
input on a
modern TV, resistance wise? It is working ok - but
making the short
circuit light come on on the aerial DA. It does indeed
read short
circuit. The Topfield PVR reads approx 175 ohms, and
having that before
the TV seems to work fine. But I'm wanting to move
things around so
this won't be possible.

I'm surprised that the inner-to-outer reads a low DC
resistance. As you
have found, this may compromise the working of any
equipment connected
to it. I would expect it to DC blocked - probably with a
high-resistance
static discharge leak. On the other hand, does the TV set
aerial input
have the option of providing line power (5 or 12V)? Maybe
that is
complicating things.


I've just checked a Humax PVR and that is the same - a
dead short to DC.
So perhaps a transformer of some sort on the input?

This all came about because I happened to be where the DA
is and saw the
red 'short' light on - but it does still seem to work ok
like that. But is
definitely the TV causing it as it goes out if I unplug
it - but leave the
circuit to it from the DA plugged in. Including the fly
lead from wall
plate to TV.



It could be a balun for matching but I would guess more
likely a small inductor across the input that will not cause
any problems with signal but which will bleed away any
static that has built up on the aerial due to wind friction.


--
Woody

harrogate three at ntlworld dot com


  #5  
Old December 28th 13, 07:56 PM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default Aerial input.

Dave Plowman (News) wrote:
What would you expect to measure across the UHF aerial input on a modern
TV, resistance wise? It is working ok - but making the short circuit light
come on on the aerial DA. It does indeed read short circuit. The Topfield
PVR reads approx 175 ohms, and having that before the TV seems to work
fine. But I'm wanting to move things around so this won't be possible.


At one time it had to read infinity because of the isolation. Other than
that, I can tell you that when a tenant connected a downlead into his
kid's bedroom and strapped it across the distribution trunk, the 55VAC
melted the downlead. No idea what it did to the telly.

Bill
  #6  
Old December 28th 13, 11:04 PM posted to uk.tech.digital-tv
Graham.[_2_]
external usenet poster
 
Posts: 1,500
Default Aerial input.

On Sat, 28 Dec 2013 20:56:42 +0000, Bill Wright
wrote:

Dave Plowman (News) wrote:
What would you expect to measure across the UHF aerial input on a modern
TV, resistance wise? It is working ok - but making the short circuit light
come on on the aerial DA. It does indeed read short circuit. The Topfield
PVR reads approx 175 ohms, and having that before the TV seems to work
fine. But I'm wanting to move things around so this won't be possible.


At one time it had to read infinity because of the isolation. Other than
that, I can tell you that when a tenant connected a downlead into his
kid's bedroom and strapped it across the distribution trunk, the 55VAC
melted the downlead. No idea what it did to the telly.

Bill



VHS recorders were routinely supplied with isolated RF cables. Belt
and braces.
--
Graham.


%Profound_observation%
  #7  
Old December 28th 13, 11:10 PM posted to uk.tech.digital-tv
Dave Plowman (News)
external usenet poster
 
Posts: 5,342
Default Aerial input.

In article ,
Bill Wright wrote:
Dave Plowman (News) wrote:
What would you expect to measure across the UHF aerial input on a
modern TV, resistance wise? It is working ok - but making the short
circuit light come on on the aerial DA. It does indeed read short
circuit. The Topfield PVR reads approx 175 ohms, and having that
before the TV seems to work fine. But I'm wanting to move things
around so this won't be possible.


At one time it had to read infinity because of the isolation. Other than
that, I can tell you that when a tenant connected a downlead into his
kid's bedroom and strapped it across the distribution trunk, the 55VAC
melted the downlead. No idea what it did to the telly.


Nothing like that here - just an ordinary domestic aerial DA. I've got
loads of signal so I suppose I could just add a small cap inline to remove
the DC path. And extinguish that fault LED.

--
*I speak fluent patriarchy but it's not my mother tongue

Dave Plowman London SW
To e-mail, change noise into sound.
  #8  
Old December 28th 13, 11:51 PM posted to uk.tech.digital-tv
Graham.[_2_]
external usenet poster
 
Posts: 1,500
Default Aerial input.

On Sun, 29 Dec 2013 00:10:54 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Bill Wright wrote:
Dave Plowman (News) wrote:
What would you expect to measure across the UHF aerial input on a
modern TV, resistance wise? It is working ok - but making the short
circuit light come on on the aerial DA. It does indeed read short
circuit. The Topfield PVR reads approx 175 ohms, and having that
before the TV seems to work fine. But I'm wanting to move things
around so this won't be possible.


At one time it had to read infinity because of the isolation. Other than
that, I can tell you that when a tenant connected a downlead into his
kid's bedroom and strapped it across the distribution trunk, the 55VAC
melted the downlead. No idea what it did to the telly.


Nothing like that here - just an ordinary domestic aerial DA. I've got
loads of signal so I suppose I could just add a small cap inline to remove
the DC path. And extinguish that fault LED.


You can get f-type isolators
http://www.matchmaster.com.au/commer...tools/18mm-db1

My guess is if that amp goes to the trouble of turning an indicator
LED on it will also limit the current and be perfectly happy to
operate that way continuously.
--
Graham.


%Profound_observation%
  #9  
Old December 29th 13, 04:18 AM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default Aerial input.

Dave Plowman (News) wrote:

I've got
loads of signal so I suppose I could just add a small cap inline to remove
the DC path. And extinguish that fault LED.


No reason why an isolating cap would reduce the signal significantly.
CPC sell little 'f' type DC isolators. Or you could simply fit an
isolating wallplate.

Bill
  #10  
Old December 29th 13, 04:21 AM posted to uk.tech.digital-tv
Bill Wright[_2_]
external usenet poster
 
Posts: 9,381
Default Aerial input.

Bill Wright wrote:

No reason why an isolating cap would reduce the signal significantly.
CPC sell little 'f' type DC isolators.


CPC CN07153

Bill
 




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