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Dumb question: aerial connections to TV



 
 
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  #21  
Old October 1st 18, 10:49 AM posted to uk.tech.digital-tv
Mark Carver[_2_]
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Default Dumb question: aerial connections to TV

On 30/09/2018 20:19, Bill Wright wrote:
On 30/09/2018 16:43, R. Mark Clayton wrote:

If the signal is good you can use a resistive splitter.* ~-4.5dB £1
pound shop


More like 5 to 8dB


On paper it can't be any better than 6dB, can it ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #22  
Old October 1st 18, 11:49 AM posted to uk.tech.digital-tv
Ian Jackson[_7_]
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Default Dumb question: aerial connections to TV

In message , Mark Carver
writes
On 30/09/2018 20:19, Bill Wright wrote:
On 30/09/2018 16:43, R. Mark Clayton wrote:

If the signal is good you can use a resistive splitter.* ~-4.5dB 1
pound shop

More like 5 to 8dB


On paper it can't be any better than 6dB, can it ?

If a minimum-loss 2-way resistive split (whether star or delta) is
back-matched at all three ports, the theoretical loss is indeed 6dB.

If it is a star, there should be three 25 ohm resistors. However, at the
expense of back-matching, the loss can be lowered by reducing the
'input' resistor - the lowest value of zero obviously giving the lowest
loss and the worst match.

[The same can be applied to a delta split, where the two input-output
resistors can be reduced.]

I've seen some 'budget' splitters like this.

I'm busy at the moment, so I'll leave it to others to do the
calculations!
--
Ian
  #23  
Old October 1st 18, 04:30 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,079
Default Dumb question: aerial connections to TV

On 01/10/2018 09:49, Mark Carver wrote:
On 30/09/2018 20:19, Bill Wright wrote:
On 30/09/2018 16:43, R. Mark Clayton wrote:

If the signal is good you can use a resistive splitter.* ~-4.5dB £1
pound shop


More like 5 to 8dB


On paper it can't be any better than 6dB, can it ?

No but component tolerance and poor build quality often give one leg at
less than 6 and the other at more than 6. And sometimes both legs are
10dB or worse!

Bill
  #27  
Old October 2nd 18, 06:19 PM posted to uk.tech.digital-tv
Woody[_4_]
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Posts: 1,968
Default Dumb question: aerial connections to TV

On Sun 30/09/2018 13:17, Another John wrote:
Sorry for interrupting this august body with a question so simple but ...

Our TV (Sony Bravia) gets its aerial feed via the PVR (Humax Fox T2).

Owing to its continuing Green Screen problems, the Humax is frequently
powered off (via the switch on the back of the box).

The TV picture then degrades, until lost completely, so we have to
switch the Humax back on.

My dumb question: why does the aerial need the power on, to connect
through to the TV?


Going back to many yonks ago, if the split is resistive then the loss
will be 6dB, but if its a ferrite transformer variety ISTR the loss was
around 3.5dB. Is that right Bill?



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Woody

harrogate three at ntlworld dot com
  #28  
Old October 2nd 18, 06:35 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,079
Default Dumb question: aerial connections to TV

On 02/10/2018 17:19, Woody wrote:
On Sun 30/09/2018 13:17, Another John wrote:
Sorry for interrupting this august body with a question so simple but ...

Our TV (Sony Bravia) gets its aerial feed via the PVR (Humax Fox T2).

Owing to its continuing Green Screen problems, the Humax is frequently
powered off (via the switch on the back of the box).

The TV picture then degrades, until lost completely, so we have to
switch the Humax back on.

My dumb question:* why does the aerial need the power on, to connect
through to the TV?


Going back to many yonks ago, if the split is resistive then the loss
will be 6dB, but if its a ferrite transformer variety ISTR the loss was
around 3.5dB. Is that right Bill?



In theory yes.

Bill
  #29  
Old October 2nd 18, 09:00 PM posted to uk.tech.digital-tv
Terry Casey[_2_]
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Posts: 858
Default Dumb question: aerial connections to TV

In article ,
says...

On 02/10/2018 14:43, Terry Casey wrote:
In article ,
says...


Signal here from Emley Moor, 16 miles away on a log periodic aerial: 18dBmV
Loss on an eight way inductive splitter is 12dB so we have eight feeds
at 6dBmV.
Loss on each of eight eight-way splitters is 12dB so we have 64 feeds at
-6dBmV.


I find your splitter loss figures interesting.

The specifications for all the 8-way splitters I used at the
Dulwich Museum quote a worst case loss from 5 - 865MHz of
10.5dB so, for planning purposes I rounded it up to 11dB.


What make and type were they?


Comega and Tratec 4-way and 8-way. The DCs were Tratec but the
tap is not in the signsal path so through loss below 1dB

They were all 5-865MHz types or, from memory, some might have
been specified up to 1000MHz but as the highest channel of
interest is E33 (567.25MHz) it made no difference.

As for specific type numbers, all that I had were donated to
the museum, so I've none to look at here and it would really
mean a trip to the museum to check the splitters there but, as
it now a 300 mile return trip, I won't be doing that anytime
soon - if ever!

--

Terry

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