OTA HD signal interfering with cable signal - AVS Forum
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post #1 of 14 Old 12-29-2013, 03:22 PM - Thread Starter
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I have basic cable (no cable box) with Time Warner Cable. Recently, on several of the local network affiliate stations, the cable signal has begun to break up significantly. This situation started with one station and is now occurring with two more. In one case the broadcast never makes it to the screen. All I get on this station is "No Signal", or error messages.

The TWC service tech tells me the cable signal is clear, the problem is with the local OTA HD signal interferring with the cable signal. He tells me that my "older" (<5 years) Sharp Aquos set does not have proper shielding around the coax cable input which allows the OTA signal to interfere with the cable signal. His recommendation was to put foil around the coax cable input area to block the OTA signals. Or, buy a new TV.

The foil has had no affect. So, am I getting a straight story from TWC, or is there indeed OTA Interference? If the latter, any suggestions as to how I can address this problem?

Thanks for your insights.
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post #2 of 14 Old 12-29-2013, 03:35 PM
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Some posters have complained about interference from nearby Verizon LTE cell towers.

See: http://www.avsforum.com/t/1489000/lte-interference-to-twc-channels-5-1-50-1-1501

Also see this website: http://www.wral.com/4g-lte-cable-1-big-problem/13087689/
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post #3 of 14 Old 12-29-2013, 04:10 PM
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Quote:
The TWC service tech tells me the cable signal is clear, the problem is with the local OTA HD signal interferring with the cable signal. He tells me that my "older" (<5 years) Sharp Aquos set does not have proper shielding around the coax cable input which allows the OTA signal to interfere with the cable signal.
That has got to be one of the dumbest comments I've ever heard from a cable tech, surprised he didn't tell you to put the aluminum foal on your head too! Do you have TV transmitters you can see out of your window? If you unplug the cable, does your TV pull in stations with nothing plugged into the coax port? I'm not buying it, sounds like cable problem to me, otherwise you would have had this problem from day 1 and not have it appear later on.

As for LTE interfering with OTA that I can see happening.
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post #4 of 14 Old 12-29-2013, 05:06 PM
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Back in the analog day this was a common problem with cable TV. If the cable system put local channels on the same channel that they were transmitted over the air the TV would receive both if the cable was not perfectly shielded. It would cause ghosts and vertical bars and such. However now I do not believe that cable companies ever use the OTA frequency for the locals on digital cable. By the "no signal" message quoted, I assume we are discussing digital cable? Even if the problem is with analog cable the only way I could see the cable company using the OTA frequency would be on the VHF channels. It is very unlikely they would be using the same UHF frequencies as OTA. Yes, cable guys will tell you anything.
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post #5 of 14 Old 12-29-2013, 06:44 PM
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Quote:
Originally Posted by fibaldwin View Post

I have basic cable (no cable box) with Time Warner Cable. Recently, on several of the local network affiliate stations, the cable signal has begun to break up significantly. This situation started with one station and is now occurring with two more. In one case the broadcast never makes it to the screen. All I get on this station is "No Signal", or error messages.

The TWC service tech tells me the cable signal is clear, the problem is with the local OTA HD signal interferring with the cable signal. He tells me that my "older" (<5 years) Sharp Aquos set does not have proper shielding around the coax cable input which allows the OTA signal to interfere with the cable signal. His recommendation was to put foil around the coax cable input area to block the OTA signals. Or, buy a new TV.

The foil has had no affect. So, am I getting a straight story from TWC, or is there indeed OTA Interference? If the latter, any suggestions as to how I can address this problem?

Thanks for your insights.

What town do you live in?
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post #6 of 14 Old 12-30-2013, 04:34 AM - Thread Starter
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Originally Posted by ejb1980 View Post

What town do you live in?

Cary, a suburb of Raleigh, NC.
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post #7 of 14 Old 12-30-2013, 05:17 AM
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Do you see similar breakup on any other channels besides the locals? There are usually a few "cable" channels, like home shopping, local government or educational channels, religious, NASA or C-SPAN, that are still cablecast in the clear.
I'd be very surprised if the local broadcast channels are ALL exactly on the same cable channels as they broadcast OTA on.

As a "fix", though, you could try a few (2 to 4 should do it) of those Radio Shack "snap-on" ferrite torroids on the cables. Try a couple on the coax, then try adding a couple on the power cord.
This may help some. For best results, you might have to order some that are made for the UHF frequencies, though. The RS ones are "tuned" (via their chemical composition, o r "mix") to frequencies of about 25 to 250 MHz.....basically VHF.
A company like Amidon Associates, or Palomar can help you select the correct ones:

sales@amidoncorp.com
sales@Palomar-Engineers.com

Your Cable company ought to be able to give you a list of what actual channels are carrying the affected signals.

Ken English, Sr. Engineer, KSL-TV.
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post #8 of 14 Old 12-30-2013, 05:38 AM - Thread Starter
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Originally Posted by kenglish View Post

Do you see similar breakup on any other channels besides the locals?
The problem does seem to be isolated to the local stations. For example, I have no issues with the ESPN channels or Comedy Central.

Thanks for your recommendations, Ken.
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post #9 of 14 Old 12-30-2013, 05:49 AM
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Quote:
Originally Posted by fibaldwin View Post

I have basic cable (no cable box) with Time Warner Cable. Recently, on several of the local network affiliate stations, the cable signal has begun to break up significantly. This situation started with one station and is now occurring with two more. In one case the broadcast never makes it to the screen. All I get on this station is "No Signal", or error messages.

The TWC service tech tells me the cable signal is clear, the problem is with the local OTA HD signal interferring with the cable signal. He tells me that my "older" (<5 years) Sharp Aquos set does not have proper shielding around the coax cable input which allows the OTA signal to interfere with the cable signal. His recommendation was to put foil around the coax cable input area to block the OTA signals. Or, buy a new TV.

The foil has had no affect. So, am I getting a straight story from TWC, or is there indeed OTA Interference? If the latter, any suggestions as to how I can address this problem?

It's not the local OTA causing problems, it's Verizon LTE.

http://www.wral.com/4g-lte-cable-1-big-problem/13087689/

- Trip

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post #10 of 14 Old 12-30-2013, 06:13 AM - Thread Starter
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Originally Posted by Trip in VA View Post

It's not the local OTA causing problems, it's Verizon LTE.

http://www.wral.com/4g-lte-cable-1-big-problem/13087689/

- Trip

Very interesting, thanks Trip! This may be nitpicking, but the article references set-top boxes not properly shielded. I don't have a set-top box. So, does the LTE interfere at via the coax cable, the cable junction on the TV, both? Other than choosing between my phone or my TV, are there any viable options that will allow me to use both?

Thanks very much for the insight.
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post #11 of 14 Old 12-30-2013, 06:25 AM
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I suspect it's either in the receive portion of the TV itself, or at the connector. You may want to check that the connectors are all tightly screwed in and that the connectors themselves are correctly fastened to the end of the coax.

- Trip

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post #12 of 14 Old 12-30-2013, 06:53 AM
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Another thing to check is the coax. If it is RG59, that coax is not shielded that well. Then try to check all the coax for cracks, cuts, or homemade splices.
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post #13 of 14 Old 12-30-2013, 11:28 AM
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Looks like Radio Shack has an LTE filter available (only on-line).......Probably not what you need right here, but could be useful for OTA, if the signal is strong enough, or close enough, to cause intermod.

Now, what I wish is, that Radio Shack would come out with some UHF ferrites, and carry those (and the filters) in their stores.

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post #14 of 14 Old 12-30-2013, 11:41 AM
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Moderately technical article, here:

http://www.rohde-schwarz-av.com/_pdf/Application%20Notes/Interference/CATV%20-%20LTV%20Interference%20App%20Note.pdf

Ken English, Sr. Engineer, KSL-TV.
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