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Discussion Starter · #1 ·
I am a new forum user and have been unable to find information on the following issue. I've read through most of the WBBM DT (CBS Chicago) posts and have searched the forum and not found this issue specifically addressed. If I've missed something, please point me in the right direction.


I encounter interference with the WBBM DT OTA signal when any electrical appliance is switched on or off in my house, including light switches. The interference causes pixelation and/or picture freeze. The interference also interupts the audio, which takes a second or two to reset through my receiver. Is there anything that can be done to reduce/eliminate this interference?


I live in Streamwood IL and am using a Zenith HDV420 tuner with an attic mount attenna. Signal strenght for all Chicago DT channels is in the normal to high range, including WBBM. I do not encounter the interference on any of the other stations. My house is only 4 years old, so I hope all of the wiring is up to code.


Thanks in advance for your replys.
 

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There are a couple of things you can try.


The easiest is to pick up a Monster Power surge protector that has line conditioning on it. These come in three levels, and any of them might do the trick. Buy from a place with a good return policy if they don't work for you.
 

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The interference is more likely RFI and coming over the air than over the electrical lines. I've been playing with an attic antenna and it has the same problem. When I went back to the outside antenna, the problem virtually disappears. Low VHF is especially susceptible to impulse noise. Getting the antenna away from household sources of electrical noise is one solution. Some people with attic antennas have had success mounting the antenna as high as possible and using foil backed insulation with the foil facing down. Electrical sparks from motor brushes and switch contacts making and breaking generate RFI.
 

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I doubt that the interference signal is coupling through your power cord. Something is probably coupling to your antenna or your antenna cable. Are you using coaxial cable or twinax? Coaxial is better.


Check the routing of your antenna cable. Is it possible that your antenna cable is routed right next to a power cable for long parallel runs? If so, separate them as much as possible. If not, then moving your antenna, as the other poster recommended, should do the trick. Let us know how it works.
 

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After many months of "blaming" WBBM, I read this post and discovered I have the same problem. Any device that is on the same branch as my system will cause an audio dropout (and sometimes video pixelation) when switched on/off rapidly.


I'm running my system off of a APC 1400 battery backup, so I don't yet know if the noise is being coupled thru the power line. I can see electrical noise on all channels if I switch to SD using my VCR, but only WBBM has this problem on HD.


Antenna is attic mounted, RG6 (~35'), grounded at cold water pipe (same point as electrical service), no power/conduit within 6' of run. Receiver is the same as yours Zenith HDV420.



Let us know if you find a solution and I'll do the same.


The quest begins...
 

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I have EMF interference on WBBM Ch. 2 as well. It is of the random white pixel variety.


How close does the cable have to be to an electrical conduit for there to be a problem. My cable is parrallel to my conduit for a 15 foot run, but the cable is on the outside of the house, and the conduit is in the wall. I would think that having the electrical in a conduit in and of itself would eliminate EMF, but what do I know?


Anybody think that there is a connection between EMF and running the signal through the vcr? I do the same thing.


I have a really half assed antenna/ cable ground. Besides rerouting my cable, I will be grounding everything to the electric system ground at some point this spring.
 

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Eric,


Don't be concerned about wiring in metal conduit. Do be concerned about proper grounding.
 

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Discussion Starter · #9 ·
Sorry, I've been away from the forum for a while. My antenna run (RG6 for about 60') crosses a few conduits in the attic and is parallel for about the last 10 feet. I pulled the antenna line through the wall next to the existing cable and there is a power outlet running down the same wall about a foot away.


I haven't tried the foil backed insulation idea yet, not sure how much I will need. I already have the antenna hanging from the peak inside the attic, so I can't go higher. If I move the antenna around I start losing signal strength.


If I try the foil backed insulation I'll let you know if it helps.


Thanks for the feedback.
 

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Just wait until the summer thunderstorm season starts. You'll be able to detect lightning strikes from 20 miles away as the storms roll through by counting the number of pixelation events on WBBM. Low VHF really isnt a good place for DTV.


My house has the same problem. In particular, every time I turn the ceiling fan off (not on) WBBM drops out for a few seconds. The relay in the heating thermostat does the same thing. Its not related to the wiring at all. its just RF propagation through the air caused by the arcing of the switch's contacts. Due to weak WBBM signal, the RF caused by the arc is able to interfere.


And then there's the areawide noise storms that seem to affect both WBBM and WMAQ. It was a few weeks back and I was watching CSI when the digital signal just disappeared. Turned to the analog signal and there was the most horrendous case of electric noise I ever saw. WMAQ also had it but to a lesser extent. I just figured someone in my neighborhood had turned on an arcwelder:)... Later after talking to friends, they saw the same thing only they lived in Glenview and I live in Woodstock so it was region wide. It lasted all evening and by the next day all was well again.
 

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This post is not a joke. Have someone watch your TV on analog broadcast channel 2. Go to each of the nearest telephone poles and hit them with a sledge hammer. If they see a burst of more white speckles on channel 2 analog when you do that, then the transformer on that pole is contributing to your problem. How you then go about convincing the power company to do something about it without risking incriminating yourself for causing the problem with your act of vandalism is something I leave up to your own ingenuity and guile.
 

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Mike,


What is it about the transformer that causes RF? There is no open arc in a transformer, it is an inductive device (magnetic fields).


Keep in mind that the "bad" transformer could be on any utility pole in a one block radius. I wonder what your neighbors will think when they see you in their yard beating their ultilty pole with a sledgehammer?!?


They will probably come out and want to take a whack!


Will a more directional antenna (on the roof, of course) help with RF interference from open arcs in the house? I mean, what is the gain from a signal below the antenna? It has to be pretty low, right?
 

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I guess there is something in a defective transformer installation that can arc. I'm not a "pole man" and can't bear witness to the specific malfuntion that results in the interference that occasionally comes from them.


Even the most directional VHF low-band antennas are not very directional. Most of my high-rise customers use Blonder Tongue, 5 element Yagi-style low band antennas. They all produce gobs of white speckles.


Interference attacking an antenna from the underside is basically seeing a dipole. Adding director elements to the boom will probably have little or no effect on signals hitting it from underneath.
 

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When performing a series of attic antenna experiments, having the antenna above my bedroom would cause picture and sound dropouts whenever I turned either of 2 low voltage bedside reading lamps on or off. Moving the antenna to the other end of the attic would only cause the sound to drop out when the left side lamp was turned off. An outdoor antenna at the far end of the house was immune. No other channel was affected but WBBM. It's a textbook example of dipole meeting RF.
 
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