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kenwstr

HDMI shielding?

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Hi,

Since connecting a BDP to my TV via HDMI, I always get poor to nil broadcast reception if the BDP is still switched on.

I just read an article about HDMI cable shielding.  To paraphrase, when the cable shield is connected to the HDMI plug shell via a long pigtail, this shield connection will have higher impedance.  As frequency increases, so too does impedance so, by the time we get to high frequencies such as RF, the shield is in effect disconnected.  If this is true, it explains why my TV reception is poor to non-existent whenever the BDP is turned on.  Now I have 3 questions.

 

1. Is this commonly known to be true?

2. Do some cable brands have documented better RF shielding than others?

3. Can someone please recommend an HDMI cable brand and model that is proved to effectively shield RF from influencing nearby devices?

 

Regards,

Ken

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Most HDMI cables on the market today have good shielding. I'm yet see any documentation on HDMI shielding. its always best to keep HDMI cables away from other types of cables, this can be the cause of interference its not usually the equipment.

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On 14/08/2018 at 5:14 PM, kenwstr said:

Hi,

Since connecting a BDP to my TV via HDMI, I always get poor to nil broadcast reception if the BDP is still switched on.

I just read an article about HDMI cable shielding.  To paraphrase, when the cable shield is connected to the HDMI plug shell via a long pigtail, this shield connection will have higher impedance.  As frequency increases, so too does impedance so, by the time we get to high frequencies such as RF, the shield is in effect disconnected.  If this is true, it explains why my TV reception is poor to non-existent whenever the BDP is turned on.  Now I have 3 questions.

 

1. Is this commonly known to be true?

2. Do some cable brands have documented better RF shielding than others?

3. Can someone please recommend an HDMI cable brand and model that is proved to effectively shield RF from influencing nearby devices?

 

Regards,

Ken

 

Does the interference happen with no HDMI cable and BDP powered on?  If so it’s not the HDMI cable. In any event, your shielding for your TV’s RF feed from the antenna seems inadequate. It’s best to have RG6 cable from the wall to TV to eliminate signal interference.

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I have done some testing around that now and it seems to be associated with with component coms compatability. I can get the BDP in a state where it doesn't interfere with broardcast reception but is also can't be controled properly in that state.  The BDP quick start setting has changed function.  Origionally, if it was on, the BDP was in standby mode, so ready to play as required,  In this state, proardcast reception is impaired.  The solution was to turn quick start off.  With it off, changing the TV input to HDMI would auto boot the BDP and changing the TV input to broadcast would turn off the BDP.  While this was slowish compared to quick start, it did prevent the broadcast interference problem.  Since an update, the current function is that the auto off doesn't work anymore so I have to do a more manual process to shut the BDP down before switching back to TV broadcast.

 

To answer the question, if the BDP is on and impairing TV reception, unpluging HDMI does restore TV reception.  However, as before, If the BDP is in a weird comms state, there is no interference.  That state can be produced by not following the correct procedure to maintain proper remote control of the devices.  It's just too complicated to explain Samsung TV, Sony BDP interaction but having unplugged and then reconnected HDMI is just one thing that will produce this state.  Obviously not a normally procedure.

 

Regards,

Ken

Edited by kenwstr

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Posted (edited)

My previous comments were for my home system.

 

I am also involved with a PA team.  Recently we upgraded the PA system's AV side  to  use HDMI over cat6 to projector.  The audio side of the PA system has for some time included a wireless mic.  The wireless receiver displays AF & RF levels for each of it's 2 different wireless frequency channels.  Now, whenever we pass signal over the new HDMI system, both wireless RF metres jump up indicate the same RF level on both frequencies.   I moved the antennas around to find the position of maximum RF interference.  It's definitely the HDMI cables.  Looking at this HDMI system, I suspect there is no grounding point for the HDMI.  I will take a meter in next time to check if that is the case.   It seems pretty common to run devices off external plug packs which of course means no grounding and yes, this was installed by a professional AV company.   I am not sure if this is causing any noticeable issues on the PA but, generally RF is the enemy of PA so I am not impressed but there are some strategies for dealing with it.

 

In any case, it proves that HDMI can leak copious RF.

 

Ken

 

Edited by kenwstr

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They can leak but its rare, depends on the quality of cable insulation used, buy another HDMI cable to test.

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Is the RF coming from the HDMI or the CAT6 or the converter boxes?

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On 29/08/2018 at 10:50 AM, kenwstr said:

I have done some testing around that now and it seems to be associated with with component coms compatability. I can get the BDP in a state where it doesn't interfere with broardcast reception but is also can't be controled properly in that state.  The BDP quick start setting has changed function.  Origionally, if it was on, the BDP was in standby mode, so ready to play as required,  In this state, proardcast reception is impaired.  The solution was to turn quick start off.  With it off, changing the TV input to HDMI would auto boot the BDP and changing the TV input to broadcast would turn off the BDP.  While this was slowish compared to quick start, it did prevent the broadcast interference problem.  Since an update, the current function is that the auto off doesn't work anymore so I have to do a more manual process to shut the BDP down before switching back to TV broadcast.

 

To answer the question, if the BDP is on and impairing TV reception, unpluging HDMI does restore TV reception.  However, as before, If the BDP is in a weird comms state, there is no interference.  That state can be produced by not following the correct procedure to maintain proper remote control of the devices.  It's just too complicated to explain Samsung TV, Sony BDP interaction but having unplugged and then reconnected HDMI is just one thing that will produce this state.  Obviously not a normally procedure.

 

Regards,

Ken

Sounds like an HDMI handshake issue Ken. This can occur where you're trying to control more than one component via HDMI. I'd go into the menus and switch this feature off and then see how you go.

 

I get what you're attempting to do, but there's often quite a difference between what it's supposed to do and what it actually does. The problem with HDMI handshakes is that quite often the "instruction" gets lost in translation. This especially true when using products from different manufacturers.

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On 12/06/2019 at 9:20 AM, DJGopal said:

Is the RF coming from the HDMI or the CAT6 or the converter boxes?

Well,  the Cat6 is much further away from the receiver than the HDMI signal path.  At the moment I can only test with the radio receivers dual aerials and they cover at least 30 cm which is much bigger than components like the audio extractor but it does seem to be a consistent strength from source right through the length of HDMI cabling that I can access without taking the installation down and reassembling elsewhere.  I can't get the aerials near the cat6 to test for RF there but the RF does jump up significantly near the HDMI path.  So that at least is a problem.  Yes, I need to test more extensively.

 

I think next thing I want to do when I can get into the venue again, is to test shield continuity through out the HDMI signal path and then to supply ground.  My understanding is that if it isn't grounded, then the shielding is ineffective.

 

If I find the shield isn't grounded, then I'll put in a grounding test lead, power up, play video and check the RF meters for any change.

 

If there is still no change, I guess the next step will be looking for better shielded cables.  Worst case is installing grounded cable ducting.  I have to say the installer supplied cables look cheap to me.

 

 

I think this will get me where I want to be with the PA but I thought I'd mention the confirmation of RF leakage from HDMI as I suspect it may be a factor in my original problem with my home system.  However the home system is largely packed away now due to renovations in progress.  I just have the TV and PDB setup together without the HDACC or stereo system.  At the moment, that is working fine without any of the issues above.  I think the HDACC may have been disrupting HDMI comms  and I had 3 devices sharing the aerial so the signal was more marginal and therefore more likely to be disrupted by interference from say the HDMI cabling.  So I gues, that gives me some clues to address all that once the renos are completed.

 

Ken

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I had a similar problem 10 years ago. Turned out being the wifi aerial on denon 4308. Disconnected the aerial and problem gone.

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Posted (edited)
On 13/06/2019 at 10:38 PM, spewka said:

I had a similar problem 10 years ago. Turned out being the wifi aerial on denon 4308. Disconnected the aerial and problem gone.

My problem with the PA only occurs while there is an HDMI bit stream playing.  If play is stopped, the receiver detects no RF.  Given it is also strongest nearest anything HDMI, it seems a safe bet that this is the source and likely to include the cat6.  This kind of issue is generally associated with a grounding problem,   I have only 0.1 ohms through the entire length of HDMI shield but 3.5 ohms from there to the power plug earth pin.  Who knows what the supply ground is like.  I did some checking around the desk system and found that the PA gear is not grounded through the supply ground.  Rather everything is finding ground through the interconnect signal shields and then through 2 connected PCs to the supply ground.  So, ground currently relies on 2 cheap RCA-3.5 mm TRS cables.  connecting obsolete PCs to the mixer.  One of those PCs is decommissioned and is to be removed pending team adoption of the new laptop/HDMI.  The other PC is used for audio only and is to be replaced.  The replacement plan at this point included running audio via a pro USB DAC to XLR.  As XLR is balanced it is intended to lift ground to decouple the PA from spurious PC ground noise.  This however would leave the HDMI shield floating.  I expect that will make the problem worse, will test that today and go from there but, it's looking like an HDMI specific ground will be needed.

 

I have a bit of work to do.

It will take some time.

 

Ken

Edited by kenwstr

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