# Need Help With Electrical Interference OTA



## crazypat (Mar 10, 2006)

I'm having a problem with my OTA setup. Two of my VHF channels will pixelate and sometimes lose their signal altogether when my furnace runs or when my wife uses the vacumm cleaner or her hair dryer. I'm using a medium size directional UHF/VHF roof mounted antenna with a Radio Shack 30db preamp fed into a Dish Network 622 Receiver. Both stations are about 50 miles north of my location. I'm wondering if it is the preamp that is causing the interference or the receiver. Would any kind of line conditioner help. Some time back I read of someone else having the same problem when his refrigerator was running but I couldn't locate the thread again to see if he got any help. Any suggestions would be greatly appreciated.


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## Tower Guy (Jul 27, 2005)

crazypat said:


> I'm having a problem with my OTA setup. Two of my VHF channels will pixelate and sometimes lose their signal altogether when my furnace runs or when my wife uses the vacumm cleaner or her hair dryer. I'm using a medium size directional UHF/VHF roof mounted antenna with a Radio Shack 30db preamp fed into a Dish Network 622 Receiver. Both stations are about 50 miles north of my location. I'm wondering if it is the preamp that is causing the interference or the receiver. Would any kind of line conditioner help. Some time back I read of someone else having the same problem when his refrigerator was running but I couldn't locate the thread again to see if he got any help. Any suggestions would be greatly appreciated.


Generally, there are several approaches to elimination of electrical interference. The first two are more likely to be effective.

1. Eliminate it at the source. This would mean installing filters on the appliances that interfere. You may have seen such a filter on a VGA cable. You could borrow one from an old monitor, or pick one that fits the power cord from the center group of this catalog page. Snap it on the end of the cord close to the hair dryer.

http://dkc3.digikey.com/PDF/T063/1151.pdf

2. Move TV the antenna further away from the source of the interference. This might a taller mast, relocation to the other end of the house, or even to a tree out back. This works best when the antenna is aimed away from the source of the interference.

3. A higher gain antenna will get more signal from the TV stations while simultaneously receiving less interference.

In extreme situations all three methods are necessary.


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## Nick (Apr 23, 2002)

First, I would likely suspect the integrity of the shielding and/or grounding of the
signal path from your antenna to the tv set. Check, clean and finger-tighten all of
your F-type connectors and inspect the cable run(s) for damage, like cuts, sharp
bends and loose and/or frayed shielding. In a typical home environment, a properly
shielded and grounded) coaxial cable run from antenna to tv set (or stb) should _not_
admit spurious EMI. If you are using a signal-splitter, temporarily remove it to check
if that makes a difference.

Second, as a possible, but less likely culprit, is voltage drop. I would suggest you
check the voltage level at the outlet where your tv set in plugged in, both before
and during the operation of each those appliances which seem to be causing the
interferience. While you're at it, get a plug-in ground/polarity tester at a building
supply store ($5) and check the integrity of your home's electrical wiring. If a drop
in voltage does occur in conjuction with pixelation or loss of signal, try a voltage 
regulator.

Before you try other possibilities, check the basics. Good luck, and please check
back with your findings.


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## DougRuss (Oct 16, 2005)

My bet is on the Radio Shack Pre-Amp !!


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## crazypat (Mar 10, 2006)

Thanks for all the suggestions. I'm going to replace the Radio Shack preamp with a CM7777. It should be here by Wednesday. Since I work on computers on the side I do have a few of the filters that the Tower Guy recommended. I will try putting one on my furnace if the preamp doesn't do the trick. I'll keep you posted on my progress.


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## kenglish (Oct 2, 2004)

You might also try a filter (not the ferrites, mentioned above, but a power line noise filter) on the power supply for the preamp. They can often carry power line noise back in to the coax.


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## crazypat (Mar 10, 2006)

I replaced the RS preamp with the CM7777 and still have the interference. I also tried an isolation transformer (an older unit that I've had laying around) on first the preamp and then the tuner with still no luck. All the filters I have are solid ones off of VGA cables so have to unwire then rewire the furnace to put it on th power cord. I will probably be doing this sometime this weekend. I also checked all of my coax and connectors and they seem to be good. Thanks for all the suggestions.


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## crazypat (Mar 10, 2006)

I forgot to mention that I also moved the furnace breaker in the breaker panel to the other leg. This didn't help. My antenna is roof mounted on a 15 foot mast with a rotor so I won't be relocating it anytime in the near future.


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## TreeFarm (Dec 4, 2006)

Your problem is associated with motor noise sources, which may be very difficult if not impossible to quell. My guess is your VHF antenna does not have sufficient gain and the interference is being received OTA along with the desired, but weak station signals. The interference reduces the signal to noise ratio to an unacceptable level.

You may have to go to a higher gain antenna.


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## crazypat (Mar 10, 2006)

TreeFarm said:


> Your problem is associated with motor noise sources, which may be very difficult if not impossible to quell. My guess is your VHF antenna does not have sufficient gain and the interference is being received OTA along with the desired, but weak station signals. The interference reduces the signal to noise ratio to an unacceptable level.
> 
> You may have to go to a higher gain antenna.


I forgot to mention that the 2 stations I'm having trouble with are being received off the back of a medium size directional UHF/VHF/FM antenna. Would going to a larger (possibly a Channel Master) antenna help. I'm also contemplating relocating my antenna to a topped off medium sized pine tree about 20 ft. high after I top it. I live on a hill so this would raise the antenna about 25 ft. higher than were it is on the top of my house. This would require about a 300 to 400 ft. run of cable. I just wasn't sure if getting a larger antenna improved back signals as well as it does on a front directional signal. I don't receive these signals at all off the front if I rotate the antenna to face towards them. My OTA receiver is very good at locking in multipath signals which is what I'm guessing these are.


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## Tower Guy (Jul 27, 2005)

crazypat said:


> I forgot to mention that the 2 stations I'm having trouble with are being received off the back of a medium size directional UHF/VHF/FM antenna.


The two stations off the back of your antenna are attenuated by the front to back ratio of your antenna. That makes the interference worse. You could add a rotor or a second antenna. If you put your antenna 300'-400' away from the house the problem is sure to go away. You will need amplification to overcome the loss of the line plus lower loss line if you can afford it. Most installations use RG6. Longer runs work better with RG11. I also have a 400' run for stations that I receive on my tower. The line that I use is 3/4" diameter that I picked up surplus from a cable friend. The 3/4" hardline works without a preamp.


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## TreeFarm (Dec 4, 2006)

If that were my place, I would try to find a way to mount a separate VHF antenna pointed toward those stations. That would avoid the hassles of a rotator.


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## crazypat (Mar 10, 2006)

Tower Guy said:


> The two stations off the back of your antenna are attenuated by the front to back ratio of your antenna. That makes the interference worse. You could add a rotor or a second antenna. If you put your antenna 300'-400' away from the house the problem is sure to go away. You will need amplification to overcome the loss of the line plus lower loss line if you can afford it. Most installations use RG6. Longer runs work better with RG11. I also have a 400' run for stations that I receive on my tower. The line that I use is 3/4" diameter that I picked up surplus from a cable friend. The 3/4" hardline works without a preamp.


I already use a rotor but get no signal if I point towards the stations north of me. Is it possible that I'm actually receiving these station from the front of my antenna from a signal that is being bounced off the mountain that my antenna is pointed at to recieve my other stationsthat are south of me?


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## TreeFarm (Dec 4, 2006)

Thirteeneth post before the OP mentions the fact that his installation includes a rotator?


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## mikeyinokc (Jan 11, 2006)

TreeFarm said:


> Thirteeneth post before the OP mentions the fact that his installation includes a rotator?


Actually he mentioned it on the #8 post.


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## crazypat (Mar 10, 2006)

I replaced my antenna with a larger one. This seems to have fixed my problem with the electrical interference. I still plan on relocating it on the upper side of my property in hopes of pulling in 4 more stations south of me. According to antenna web this move should do the trick. I'm keeping my fingers crossed.


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