Interference between HDMI and RF leads - advice requested

I hope that my question is not OT but I know there are some people on
this forum who are expert in all aspects of digital TV and related
wiring issues.

I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

I am advised on another forum that: "The interference effect is
affected by the resolutions settings.
At certain settings the frequencies that are going through the HDMI
link are similar to certain parts of the frequencies on the UHF
waveband.
The problem appears to arise when there is perhaps a combinations of a
leaky HDMI cable which will allow these frequencies to radiate out and
leaky UHF cables which allow these frequencies to leak in, most likely
causing saturation in the tuner which activates agc circuits
[automatic gain control ] in the tuner to reduce the sensitivity of
the tuner."

I am using a good quality, HDMI lead, CT100 cable for the incoming
signal and the supplied Panasonic fly lead to connect the recorder to
the Sony Bravia TV. Everything works if I connect the units by SCART
but I lose the HD.

My question is how do I create a condition that avoids this
interference? Is there a type of cable that I can use for the RF
leads and types of termination that will minimise this interference? I
have ordered a branded Panasonoc HDMI cable so that If I cannot solve
the issue myself at least I can contact them with the position of
using all their recommended components.

I have not seen this problem mentioned before on this forum but
searches indicate it is fairly widespread but advice and solutions
seem hard to find.

"ChrisW" wrote in message
...
I hope that my question is not OT but I know there are some people on
this forum who are expert in all aspects of digital TV and related
wiring issues.

I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

Odd.

Try reversing the HDMI lead, another HDMI lead, an HDMI lead with nothing on
the other end to try and isolate the fault. Oh yes and provide an earth
somewhere.

CT100 should provide sufficient isolation for the UHF in, whether the HDMI
is shielded or not, so the symptoms you describe suggest a fault inside the
box as the HDMI is only active when something is plugged in.

At 11:33:28 Mon, 30 Aug 2010, R. Mark Clayton wrote:
"ChrisW" wrote in message
.. .
I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

Odd.

Try reversing the HDMI lead, another HDMI lead, an HDMI lead with nothing on
the other end to try and isolate the fault. Oh yes and provide an earth
somewhere.

Could a problem possibly arise from having two earthing points, creating
an earth loop that's picking up interference?

John L

In message , John Legon
writes
At 11:33:28 Mon, 30 Aug 2010, R. Mark Clayton wrote:
"ChrisW" wrote in message
. ..
I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

Odd.

Try reversing the HDMI lead, another HDMI lead, an HDMI lead with nothing on
the other end to try and isolate the fault. Oh yes and provide an earth
somewhere.

Could a problem possibly arise from having two earthing points, creating
an earth loop that's picking up interference?

Although they are not 'cure-alls', it might be worth trying one or more
clip-on ferrites on the HDMI lead (say one at each and?) - even or both
leads.
--
Ian

On Aug 30, 11:09*am, ChrisW
wrote:
I hope that my question is not OT but I know there are some people on
this forum who are expert in all aspects of digital TV and related
wiring issues.

Yes, and what we don't know we'll make up...


I have a new Panasonic HD DVD Recorder (DMR-XW380). *The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. *The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

It suggests that the interference is passing along the HDMI cable
(obviously?) and entering the recorder circuitry after (not at) the
tuner input. Otherwise I would have expected the loop- through to be
affected to some extent. However that isn't definite.


I am advised on another forum that: "The interference effect is
affected by the resolutions settings.
At certain settings the frequencies that are going through the HDMI
link are similar to certain parts of the frequencies on the UHF
waveband.
Really, the solution is likely to be prevention of the interference
path. Juggling frequencies isn't likely to provide a complete cure.

The problem appears to arise when there is perhaps a combinations of a
leaky HDMI cable which will allow these frequencies to radiate out and
leaky UHF cables which allow these frequencies to leak in, most likely
causing saturation in the tuner which activates agc circuits
[automatic gain control ] in the tuner to reduce the sensitivity of
the tuner."
No, I'd say the interference is getting from the HDMI cable to
somewhere it shouldn't within the recorder. However you can test the
'leaky cable hypothesis' by physically arranging the items so that the
RF enters the recorder and the HDMI leaves the recorder with the two
as far apart as possible. If for instance the RF input is on the RH
side of the back of the recorder and the HDMI is on the LH side, bring
the RF in from the right and take the HDMI out to the left.

I suggest you get hold of an alternative TV set and try the recorder
with that. I'm far from convinced that the interference is actually an
HDMI signal. I've never seen this fault via HMDI, but plenty of times
I've seen it via scart, and if naughty RF can get onto a TV set's
scart input from elsewhere inside the set I don't see why it can't get
onto an HDMI input. What I'm saying is, this could well be a fault on
the TV set. As I say, it's common enough for TV sets to do this via
the scart, or by actual radiation.


I am using a good quality, HDMI lead, CT100 cable for the incoming
signal
Check that the screen is making perfect contact inside the plugs at
both ends.

and the supplied Panasonic fly lead to connect the recorder to
the Sony Bravia TV.
I suggest you do all tests with the RF loopthrough removed.

Everything works if I connect the units by SCART
but I lose the HD.

My question is how do I create a condition that avoids this
interference? *Is there a type of cable that I can use for the RF
leads and types of termination that will minimise this interference? I
have ordered a branded Panasonoc HDMI cable so that If I cannot solve
the issue myself at least I can contact them with the position of
using all their recommended components.

I have not seen this problem mentioned before on this forum but
searches indicate it is fairly widespread but advice and solutions
seem hard to find.

If the problem is exacerbated by an incoming RF signal that is
anything other than superstrong, you could fit a preamp somewhere on
the RF feed. This should be well away from the TV set/recorder area.
It could be a masthead amp or a simple in-line booster. That would
certainly improve the s/n ratio.

Here are two other ideas. They aren't scientific. They assume
everything above is wrong or questionable.
Try an HDMI extension cable, so the HDMI link is really long. Try
ferrite rings on the HDMI.

Bill

" wrote in message
...
On Aug 30, 11:09 am, ChrisW
wrote:
I hope that my question is not OT but I know there are some people on
this forum who are expert in all aspects of digital TV and related
wiring issues.

Yes, and what we don't know we'll make up...


I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

It suggests that the interference is passing along the HDMI cable
(obviously?) and entering the recorder circuitry after (not at) the
tuner input. Otherwise I would have expected the loop- through to be
affected to some extent. However that isn't definite.


I am advised on another forum that: "The interference effect is
affected by the resolutions settings.
At certain settings the frequencies that are going through the HDMI
link are similar to certain parts of the frequencies on the UHF
waveband.
Really, the solution is likely to be prevention of the interference
path. Juggling frequencies isn't likely to provide a complete cure.

The problem appears to arise when there is perhaps a combinations of a
leaky HDMI cable which will allow these frequencies to radiate out and
leaky UHF cables which allow these frequencies to leak in, most likely
causing saturation in the tuner which activates agc circuits
[automatic gain control ] in the tuner to reduce the sensitivity of
the tuner."
No, I'd say the interference is getting from the HDMI cable to
somewhere it shouldn't within the recorder. However you can test the
'leaky cable hypothesis' by physically arranging the items so that the
RF enters the recorder and the HDMI leaves the recorder with the two
as far apart as possible. If for instance the RF input is on the RH
side of the back of the recorder and the HDMI is on the LH side, bring
the RF in from the right and take the HDMI out to the left.

I suggest you get hold of an alternative TV set and try the recorder
with that. I'm far from convinced that the interference is actually an
HDMI signal. I've never seen this fault via HMDI, but plenty of times
I've seen it via scart, and if naughty RF can get onto a TV set's
scart input from elsewhere inside the set I don't see why it can't get
onto an HDMI input. What I'm saying is, this could well be a fault on
the TV set. As I say, it's common enough for TV sets to do this via
the scart, or by actual radiation.


I am using a good quality, HDMI lead, CT100 cable for the incoming
signal
Check that the screen is making perfect contact inside the plugs at
both ends.

and the supplied Panasonic fly lead to connect the recorder to
the Sony Bravia TV.
I suggest you do all tests with the RF loopthrough removed.

Everything works if I connect the units by SCART
but I lose the HD.

My question is how do I create a condition that avoids this
interference? Is there a type of cable that I can use for the RF
leads and types of termination that will minimise this interference? I
have ordered a branded Panasonoc HDMI cable so that If I cannot solve
the issue myself at least I can contact them with the position of
using all their recommended components.

I have not seen this problem mentioned before on this forum but
searches indicate it is fairly widespread but advice and solutions
seem hard to find.

If the problem is exacerbated by an incoming RF signal that is
anything other than superstrong, you could fit a preamp somewhere on
the RF feed. This should be well away from the TV set/recorder area.
It could be a masthead amp or a simple in-line booster. That would
certainly improve the s/n ratio.

Here are two other ideas. They aren't scientific. They assume
everything above is wrong or questionable.
Try an HDMI extension cable, so the HDMI link is really long. Try
ferrite rings on the HDMI.

Bill

I had the same problem when connecting a BT Vision to my HD TV via HDMI.
While the Vision box was off the shelf and on the floor the signal Quality
leapt up to good from zero when I grasped the BT Vision/TV loop through
aerial lead in my hand.

My solution was to replace the loop lead with one I made up from CT100
cable, for good measure I put snap on ferrites on this lead and also on the
primary aerial feed.
Finally when putting the Vision box back in its normal position I made sure
that all aerial leads and HDMI leads were kept as far apart as space
allowed.
Result: 100% quality on all six muxes. Signal strength less than 80% which
on my kit works just fine. Reception now as good as it gets for terrestrial
TV.

Richard H

I knew I had posted in a place where I would get some helpful
suggestions! Many thanks for all the ideas. I am going to be busy
trying out the various suggestions over the next few days. I'll wait
until the Panasoninc HDMI lead arrives first but then I'll try
everything out. Now to find a source of snap- on ferrites.....

In article , ChrisW
writes
I knew I had posted in a place where I would get some helpful
suggestions! Many thanks for all the ideas. I am going to be busy
trying out the various suggestions over the next few days. I'll wait
until the Panasoninc HDMI lead arrives first but then I'll try
everything out. Now to find a source of snap- on ferrites.....

Google "clip on ferrite" and you should find plenty. Try to get one big
enough to get a couple of turns on, the effectiveness goes up
dramatically.

If you think it's the telly, put it at the telly end but one each end
will do no harm, they will not effect the signal.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

It would be interesting to see if there is some kind of standing current if
you put a piece of wire between the metal parts of plugs on both items.
I wonder if its as simple as just poor internal earthing, regardless of
most things not being earthed these days. In the old analogue days you could
tell from the signal you were left with what the cause was but on Digital it
just stops bloomin well working, giving few clues.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"R. Mark Clayton" wrote in message
...

"ChrisW" wrote in message
...
I hope that my question is not OT but I know there are some people on
this forum who are expert in all aspects of digital TV and related
wiring issues.

I have a new Panasonic HD DVD Recorder (DMR-XW380). The unit's twin
tuners find all the channels (incuding DVB-T2) and show excellent
signal strength and quality until I connect the HDMI lead between the
recorder and TV. Then the signal strength remains high but the quality
goes to zero along with the picture. The pass through signal to the
TV remains fine and all the stations are OK on the TV but non existent
on the Panasonic unit.

Odd.

Try reversing the HDMI lead, another HDMI lead, an HDMI lead with nothing
on the other end to try and isolate the fault. Oh yes and provide an
earth somewhere.

CT100 should provide sufficient isolation for the UHF in, whether the HDMI
is shielded or not, so the symptoms you describe suggest a fault inside
the box as the HDMI is only active when something is plugged in.

CPC have the ferrites, but before you rush out and buy some, do you live
near any strong on all the time transmitters, I wonder? You may just have
cable lengths of the right length to pick this up and cause mayhem in the
leaeast screenrd easy overloaded circuits.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"ChrisW" wrote in message
...
I knew I had posted in a place where I would get some helpful
suggestions! Many thanks for all the ideas. I am going to be busy
trying out the various suggestions over the next few days. I'll wait
until the Panasoninc HDMI lead arrives first but then I'll try
everything out. Now to find a source of snap- on ferrites.....