Shielded coax cable

I recently installed a new 4-output TV-link-enabled booster in a household
where the terrestrial aerial was shielded by trees which were attenuating the
signal.

This caused a problem (which existed both with the old and the new booster) on
two of their 5 sets, whereby the analogue signals had major pre-echo, because
the coax leading to each of these two sets ran horizontally along a wall which
faced Winter Hill - the coax was picking up more signal than the
aerial+booster was providing.

The owners weren't bothered by this, because they only watch Sky+ on the two
affected TVs.
However, for future reference, is there a well-shielded / high-grade type of
UHF coax cable which doesn't unintentionally pick up off-air signals in strong
signal areas?

In message , jamie powell
wrote


However, for future reference, is there a well-shielded / high-grade
type of UHF coax cable which doesn't unintentionally pick up off-air
signals in strong signal areas?


http://www.wrightsaerials.tv/articles/coax-cable-quality-hmdi-m.html
--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

"Alan" wrote in message
...
In message , jamie powell
wrote


However, for future reference, is there a well-shielded / high-grade type of
UHF coax cable which doesn't unintentionally pick up off-air signals in
strong signal areas?


http://www.wrightsaerials.tv/articles/coax-cable-quality-hmdi-m.html

Already read it. Bill's shielding (screening) tests are unscientific at best,
and in any event, are only designed to measure crosstalk between cables
running alongside each other in the same conduits.

In my example, the cable is being pelted with strong off-air signals which it
has to keep out, while preserving a weakened 'distributed' signal being
carried by the cable on the same frequencies.

"jamie powell" wrote in message
...

"Alan" wrote in message
...
In message , jamie powell
wrote


However, for future reference, is there a well-shielded / high-grade type
of UHF coax cable which doesn't unintentionally pick up off-air signals
in strong signal areas?


http://www.wrightsaerials.tv/articles/coax-cable-quality-hmdi-m.html

Already read it. Bill's shielding (screening) tests are unscientific at
best, and in any event, are only designed to measure crosstalk between
cables running alongside each other in the same conduits.

In my example, the cable is being pelted with strong off-air signals which
it has to keep out, while preserving a weakened 'distributed' signal being
carried by the cable on the same frequencies.


Take no notice of those tests. The only thing you might be able to do is
run the coax in conduit and earth it, then it will act as a shield. You
will
find it is the preamp picking up the strong signal - get one with a lower
gain.
If you were to earth the braid of the coax it wouldn't give the same
problem.
You could always move the aerial slightly and change the way the coax runs.
How about a ferrite core with a few turns of coax before the TVs, this
will stop a few problems. Each situation is different.

I would start with the ferrite core and as a last resort earthing the braid.
If the signal was strong enough to the TV you could use an attenuator
to cut down on the signal you say is being picked up on the braid of the
coax. The signal from the booster would overcome any loss.

Take no notice of those tests. The only thing you might be able to do is
run the coax in conduit and earth it, then it will act as a shield. You
will
find it is the preamp picking up the strong signal - get one with a lower
gain.
If you were to earth the braid of the coax it wouldn't give the same
problem.
You could always move the aerial slightly and change the way the coax runs.
How about a ferrite core with a few turns of coax before the TVs, this
will stop a few problems. Each situation is different.
I would start with the ferrite core and as a last resort earthing the braid.
If the signal was strong enough to the TV you could use an attenuator
to cut down on the signal you say is being picked up on the braid of the
coax. The signal from the booster would overcome any loss.
++++++++++++

Assuming that you aren't joking, the above only confirms my long held
opinion that you are a reasonably competent aerial installer with a lot of
misconceptions and a grudge. Since you install aerials every day why don't
you try to learn properly from your experience? Put aside your half-baked
theories and start from scratch. Look at everything with fresh eyes. Don't
try to make what happens fit in with your preconceved ideas. There's a
wealth of practical knowledge out there, once you are prepared to harvest
it. Read a few good articles and spend some time comparing what they say
with what you have found in the field. We are all wrong about many things,
but we should try to improve!

Bill

In my example, the cable is being pelted with strong off-air signals which
it
has to keep out, while preserving a weakened 'distributed' signal being
carried by the cable on the same frequencies.

++++++++++

Yes, I think we're fairly familiar with the concept, son.

Bill

In article , jamie powell
wrote:

"Alan" wrote in message
...
In message , jamie powell
wrote


However, for future reference, is there a well-shielded / high-grade
type of UHF coax cable which doesn't unintentionally pick up off-air
signals in strong signal areas?


http://www.wrightsaerials.tv/articles/coax-cable-quality-hmdi-m.html

Already read it. Bill's shielding (screening) tests are unscientific at
best, and in any event, are only designed to measure crosstalk between
cables running alongside each other in the same conduits.

In my example, the cable is being pelted with strong off-air signals
which it has to keep out, while preserving a weakened 'distributed'
signal being carried by the cable on the same frequencies.

In order for a co-axial cable to work as intended it is essential that it
is fed and terminated in an unbalanced way. If the aerial doesn't have a
balun then this will seriously affect the screening properties of the cable.
In wired distribution systems where direct off air break through can
happen, it is usual to carry out transposition of the received channels to
avoid interference.

--
From KT24

Using a RISC OS computer running v5.11

On 27/11/09 04:41, Bill wrote:

Assuming that you aren't joking

The Idiot has changed name again, leave him chatting with Jamie.

In article ,
jamie powell wrote:
http://www.wrightsaerials.tv/articles/coax-cable-quality-hmdi-m.html

Already read it. Bill's shielding (screening) tests are unscientific at
best, and in any event, are only designed to measure crosstalk between
cables running alongside each other in the same conduits.

Have you actually read the article? Or better, understood it?

In my example, the cable is being pelted with strong off-air signals
which it has to keep out, while preserving a weakened 'distributed'
signal being carried by the cable on the same frequencies.

Which part of 'screening' don't you understand?

--
*Welcome to **** Creek - sorry, we're out of paddles*

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 27 Nov 2009 00:54:41 -0000, "David Perry"
wrote:

Take no notice of those tests. The only thing you might be able to do is
run the coax in conduit and earth it, then it will act as a shield. You
will
find it is the preamp picking up the strong signal - get one with a lower
gain.
If you were to earth the braid of the coax it wouldn't give the same
problem.
You could always move the aerial slightly and change the way the coax runs.
How about a ferrite core with a few turns of coax before the TVs, this
will stop a few problems. Each situation is different.

I would start with the ferrite core and as a last resort earthing the braid.
If the signal was strong enough to the TV you could use an attenuator
to cut down on the signal you say is being picked up on the braid of the
coax. The signal from the booster would overcome any loss.


Could you please describe what you mean by 'earthing' in the context
of a UHF signal?
- a supply mains earth? a water pipe? a copper stake?
You are aware I suppose that an 'earthing' lead which is a multiple of
half-waves will be an open-circuit, and that half-waves are different
lengths for each channel?
You are aware that the 'earth' to which you connect it may actually be
carrying more UHF signal (and noise) that could be injected into the
signal?