A vexing problem is identified. How do I fix it?

Swerd

Swerd

Audioholic Warlord
Today I identified a small but vexing problem I’ve had with TV reception. My TV is a typical digital HD model, now several years old. I run three inputs into it:
  1. An antenna cable, roughly 50-75 feet long, connects the TV to a UHF antenna in the attic. The cable is RG-6 with the usual F connectors. Guessing by its thickness, the cable is quad shielded RG-6Q, but I’m not certain about that.

  2. An HDMI cable runs from the AVR to the TV. It delivers video from a Blu-Ray disc player.

  3. A Google Chromecast dongle also connects to an HDMI receptacle on the TV. It is fed DC power by a USB cable coming from an AC outlet. This dongle consists of a flat disc body dangling from a 4” long HDMI cable. The DC power line plugs directly into the dongle body. It's HDMI receptacle on the back of the TV is right next to several other HDMI receptacles, and the threaded post for the antenna cable.
Soon after I added the Chromecast dongle, I started having minor occasional interference problems. I would see brief pixilation on the screen and hear rapid on/off interruptions of the audio. This was usually short lived, and occurred only if I watch broadcast TV via the antenna. Sometimes it didn’t happen at all, and other times broadcast TV was unwatchable.

At first, I thought I had damaged the F connector on the antenna cable when I installed the dongle. I changed it several times, without eliminating the problem. So I knew that one day I would have to crawl into the attic and trouble shoot this problem. What could be wrong other than the antenna or the cable? Lots of procrastination followed. It always seemed too cold or too hot to go up to the attic. Other times, I was just too lazy. After all, it was only commercial TV – I don’t have cable TV – and I watch more and more video through streaming sources.

Today, the summer heat was gone, and I decided it was time to pull-down the ladder and climb into that unfinished attic. I found an old rabbit ears-type antenna and planned to attach it to antenna cable in the attic. That way, I could see if the problem was in the antenna or the cable. But before doing that, I thought it might be smart to attach those old rabbit ears directly to the TV, just to see how well it worked. That dongle was in the way, so I took it out before attaching the rabbit ears. That eliminated the interference! I replaced the attic antenna cable, but left the dongle off. I watched TV for a good hour just to see if that intermittent problem returned – it didn’t!

That identifies the problem. It was EMI from the DC-powered dongle, which is close by the antenna connection. How can I fix it and still use the dongle? I’ve got two ideas.
  • Shield the F connector at the back of the TV with aluminum foil. Also, wrap the dongle in aluminum foil.

  • Get a short HDMI extension cable, 1 to 3 feet long, and put it between the dongle and the TV. Tie the dongle down so it can't get close to the antenna cable. That way the dongle and it’s USB power cable is farther away from the F connector.

  • Do all of the above.
Does anyone have other ideas how I might fix this? @TLS Guy or @BMXTRIX or any one?
 
XEagleDriver

XEagleDriver

Senior Audioholic
I think the short HDMI cable to build more space between the two is the likely solution.

Sent from my SM-G975U using Tapatalk
 
TLS Guy

TLS Guy

Audioholic Slumlord
Today I identified a small but vexing problem I’ve had with TV reception. My TV is a typical digital HD model, now several years old. I run three inputs into it:
  1. An antenna cable, roughly 50-75 feet long, connects the TV to a UHF antenna in the attic. The cable is RG-6 with the usual F connectors. Guessing by its thickness, the cable is quad shielded RG-6Q, but I’m not certain about that.

  2. An HDMI cable runs from the AVR to the TV. It delivers video from a Blu-Ray disc player.

  3. A Google Chromecast dongle also connects to an HDMI receptacle on the TV. It is fed DC power by a USB cable coming from an AC outlet. This dongle consists of a flat disc body dangling from a 4” long HDMI cable. The DC power line plugs directly into the dongle body. It's HDMI receptacle on the back of the TV is right next to several other HDMI receptacles, and the threaded post for the antenna cable.
Soon after I added the Chromecast dongle, I started having minor occasional interference problems. I would see brief pixilation on the screen and hear rapid on/off interruptions of the audio. This was usually short lived, and occurred only if I watch broadcast TV via the antenna. Sometimes it didn’t happen at all, and other times broadcast TV was unwatchable.

At first, I thought I had damaged the F connector on the antenna cable when I installed the dongle. I changed it several times, without eliminating the problem. So I knew that one day I would have to crawl into the attic and trouble shoot this problem. What could be wrong other than the antenna or the cable? Lots of procrastination followed. It always seemed too cold or too hot to go up to the attic. Other times, I was just too lazy. After all, it was only commercial TV – I don’t have cable TV – and I watch more and more video through streaming sources.

Today, the summer heat was gone, and I decided it was time to pull-down the ladder and climb into that unfinished attic. I found an old rabbit ears-type antenna and planned to attach it to antenna cable in the attic. That way, I could see if the problem was in the antenna or the cable. But before doing that, I thought it might be smart to attach those old rabbit ears directly to the TV, just to see how well it worked. That dongle was in the way, so I took it out before attaching the rabbit ears. That eliminated the interference! I replaced the attic antenna cable, but left the dongle off. I watched TV for a good hour just to see if that intermittent problem returned – it didn’t!

That identifies the problem. It was EMI from the DC-powered dongle, which is close by the antenna connection. How can I fix it and still use the dongle? I’ve got two ideas.
  • Shield the F connector at the back of the TV with aluminum foil. Also, wrap the dongle in aluminum foil.

  • Get a short HDMI extension cable, 1 to 3 feet long, and put it between the dongle and the TV. Tie the dongle down so it can't get close to the antenna cable. That way the dongle and it’s USB power cable is farther away from the F connector.

  • Do all of the above.
Does anyone have other ideas how I might fix this? @TLS Guy or @BMXTRIX or any one?
It is RF interference from the Chromecast Dongle. Why is the dongle not plugged into your receiver rather than the TV? The dongle is transmitting the RF to the antenna cable.
 
Alex2507

Alex2507

Audioholic Slumlord
Why is the dongle not plugged into your receiver rather than the TV?
Because his old rec'r didn't have HDMI and it only recently gave up the holy smoke. Legacy wiring schemes are still in place. I gotta get to work otherwise I'd be writing jokes about our anti early adopter, Richard.
 
highfigh

highfigh

Audioholic Slumlord
Today I identified a small but vexing problem I’ve had with TV reception. My TV is a typical digital HD model, now several years old. I run three inputs into it:
  1. An antenna cable, roughly 50-75 feet long, connects the TV to a UHF antenna in the attic. The cable is RG-6 with the usual F connectors. Guessing by its thickness, the cable is quad shielded RG-6Q, but I’m not certain about that.

  2. An HDMI cable runs from the AVR to the TV. It delivers video from a Blu-Ray disc player.

  3. A Google Chromecast dongle also connects to an HDMI receptacle on the TV. It is fed DC power by a USB cable coming from an AC outlet. This dongle consists of a flat disc body dangling from a 4” long HDMI cable. The DC power line plugs directly into the dongle body. It's HDMI receptacle on the back of the TV is right next to several other HDMI receptacles, and the threaded post for the antenna cable.
Soon after I added the Chromecast dongle, I started having minor occasional interference problems. I would see brief pixilation on the screen and hear rapid on/off interruptions of the audio. This was usually short lived, and occurred only if I watch broadcast TV via the antenna. Sometimes it didn’t happen at all, and other times broadcast TV was unwatchable.

At first, I thought I had damaged the F connector on the antenna cable when I installed the dongle. I changed it several times, without eliminating the problem. So I knew that one day I would have to crawl into the attic and trouble shoot this problem. What could be wrong other than the antenna or the cable? Lots of procrastination followed. It always seemed too cold or too hot to go up to the attic. Other times, I was just too lazy. After all, it was only commercial TV – I don’t have cable TV – and I watch more and more video through streaming sources.

Today, the summer heat was gone, and I decided it was time to pull-down the ladder and climb into that unfinished attic. I found an old rabbit ears-type antenna and planned to attach it to antenna cable in the attic. That way, I could see if the problem was in the antenna or the cable. But before doing that, I thought it might be smart to attach those old rabbit ears directly to the TV, just to see how well it worked. That dongle was in the way, so I took it out before attaching the rabbit ears. That eliminated the interference! I replaced the attic antenna cable, but left the dongle off. I watched TV for a good hour just to see if that intermittent problem returned – it didn’t!

That identifies the problem. It was EMI from the DC-powered dongle, which is close by the antenna connection. How can I fix it and still use the dongle? I’ve got two ideas.
  • Shield the F connector at the back of the TV with aluminum foil. Also, wrap the dongle in aluminum foil.

  • Get a short HDMI extension cable, 1 to 3 feet long, and put it between the dongle and the TV. Tie the dongle down so it can't get close to the antenna cable. That way the dongle and it’s USB power cable is farther away from the F connector.

  • Do all of the above.
Does anyone have other ideas how I might fix this? @TLS Guy or @BMXTRIX or any one?
Any shielding would need to be grounded.
 
BMXTRIX

BMXTRIX

Audioholic Warlord
I would try various options in getting the puck as far away from the TV as possible. I would also try different scenarios of powering the puck.

The interference could be coming from the puck itself, but it could be coming from the power line, or it could be generated by the TV by using the USB connection. None of it sounds like it makes sense, but I think we've all seen situations where plugging something in one place has an impact on our audio gear. So, treat it the same way. Leave the puck where it is, but pull the USB power off the TV and plug in USB power elsewhere. See if that fixes the issue. If your AVR supports the puck, try relocating it there, even if it is only for testing. Yes, certainly try a longer HDMI cable from the puck to the TV, but leave the USB plugged into the TV. Then do it again with the puck away from the TV and the power plugged in elsewhere.

I'm not sold that the puck itself is generating enough RF interference to mess with the cable input, but I certainly could see that as the issue. But, just as likely is the power supply for USB in the TV generating internal RF which is impacting components and messing with it. So, you have a few things you can try, all of which are pretty straightforward, which could help to eliminate your issue. Since it is easier to move the USB/power connection to a new location then it may be to source a quality HDMI extension cable quickly, moving power would be the first thing I would try.
 
Swerd

Swerd

Audioholic Warlord
It is RF interference from the Chromecast Dongle. Why is the dongle not plugged into your receiver rather than the TV? The dongle is transmitting the RF to the antenna cable.
That obvious solution popped into my head only a few minutes after logging out yesterday. I hadn't yet thought of it because I was so busy trying to describe the problem.
Because his old rec'r didn't have HDMI and it only recently gave up the holy smoke. Legacy wiring schemes are still in place. I gotta get to work otherwise I'd be writing jokes about our anti early adopter, Richard.
Guilty as charged :oops:.

My old B&K AVR lacked any HDMI connections. When I installed the new Denon sometime last fall or winter, I was preoccupied with all the other cables and ignored that dongle. Those legacy wiring schemes were no longer on the rear panels, but they were still in the brain.
… The interference could be coming from the puck itself, but it could be coming from the power line, or it could be generated by the TV by using the USB connection.
The USB line was connected to an AC plug via a small USB transformer. My older Panasonic TV does not have a USB outlet.

Later today, I'll put the dongle/puck in a HDMI port on my AVR. That should solve the problem without resorting to aluminum foil. I'll keep my fingers crossed, hoping that no interference emerges.

Thanks everyone for your responses :). Even though I'm a bit embarrassed about my obtuseness, I'm still happy I didn't have to run a new antenna cable from my attic, to the basement, and up to my HT wall connectors behind the TV.
 
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Eppie

Eppie

Audioholic General
While using the AVR will likely solve the issue, those cheap AC power adapters are notorious for being noisy. Sometimes a better quality power adapter can clean things up but that does appear to be an RF issue. Probably not a whole lot of shielding around the TV connector plate.
 
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BoredSysAdmin

BoredSysAdmin

Audioholic Overlord
I second (third?) getting a different AC/USB power adapter for chromecast. For example, Amazon fireTV devices would either not work right or at all without their original power adapters as anecdotical evidence.
 
Swerd

Swerd

Audioholic Warlord
No more interference problems :).

I moved the Google Chromecast puck from the TV to an unused HDMI input on the AVR. It took me longer to look up how to make those changes in the AVR & TV manuals, than it did to actually do them.

That eliminates the RFI for TV reception, and the puck is far enough away from the AVR’s FM antenna connection so as not to create a new RFI problem. (That antenna is a low gain omni-directional antenna, also in the attic. I have many strong local FM stations.)

Everyone – thanks for your help.

FWIW, the noisy USB power adapter (as well as the USB cable) came with the Chromecast puck. I don't have to replace that. Just curious, how would I find a low-noise or RFI-free USB power adapter? Is there such a thing?
 
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TLS Guy

TLS Guy

Audioholic Slumlord
No more interference problems :).

I moved the Google Chromecast puck from the TV to an unused HDMI input on the AVR. It took me longer to look up how to make those changes in the AVR & TV manuals, than it did to actually do them.

That eliminates the RFI for TV reception, and the puck was far enough away from the AVR’s FM antenna connection so as not to create a new RFI problem. (That antenna is a low gain omni-directional antenna, also in the attic. I have many strong local FM stations.)

Everyone – thanks for your help.

FWIW, the noisy USB power adapter (as well as the USB cable) came with the Chromecast puck. I don't have to replace that. Just curious, how would I find a low-noise or RFI-free USB power adapter? Is there such a thing?
Not aware of any tests on this. I have three Chromecast devices in use, and have not had a problem with either.
 
Eppie

Eppie

Audioholic General
FWIW, the noisy USB power adapter (as well as the USB cable) came with the Chromecast puck. I don't have to replace that. Just curious, how would I find a low-noise or RFI-free USB power adapter? Is there such a thing?
EFLC in Canada carries the iFi power supplies like this one. Not that the Chromecast is necessarily bad, but in the Raspberry Pi world they are known for being supplied with cheap power adapters so many people that use hifi audio hats with their Pi usually replace the stock supply with something cleaner. If moving the Chromecast did the trick I probably wouldn't bother changing the power adapter unless you have other noise issues.
 
Swerd

Swerd

Audioholic Warlord
If moving the Chromecast did the trick I probably wouldn't bother changing the power adapter unless you have other noise issues.
Right, I'm still using the Google-supplied power adapter. The puck and it's power supply cable, were previously 2" to 3" (5 to 7 cm) away from the antenna cable's F connector. Now, they're about 3 feet (90 cm) away, and about 15" (38 cm) away from the FM antenna's connection on the back of the AVR. That weak RFI required close proximity to a vulnerable spot before it became a problem.

Now I know that interference on a digital TV looks and sounds nothing like it did on old analog TVs.
 
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