Electromagnetic Interference

Electromagnetic Interference (EMI) on TV Antenna Systems

By Ben Stallions,
Stallions Satellite and Antenna

Introduction

E lectromagnetic interference (EMI), is a type of interference that is very common in metropolitan areas and can be seen most visably on the lower VHF TV channels (2-6). Although this kind of interference can be very difficult to get rid of, knowing what causes it and how to reduce it on your TV's can be of great help.


Causes of EMI Interference

T here are two main causes of EMI interference. The first is when twinlead, a two conductor antenna lead-in wire, is used between the receiving TV antenna and the TV and/or VCR. Twinlead is the original type of downlead, but should never be used in modern TV antenna systems. Since it is not shielded, it can pickup stray interference. Instead, coaxial-type cable should be used, which has aluminum foil and braiding to reject interference.
Twinlead
Twinlead
Coaxial Cable
Coaxial Cable

The second leading cause of EMI interference on TV antenna systems is the utility poles in your neighborhood being grounded poorly. Normally this is not the fault of the power companies, but because of the ground being dry. Since water is the best form of an electrical ground, utility poles are grounded much better when the ground is wet than when the ground is dry. This kind of interference ususally disappears after it has been raining steadily for several hours and the ground is saturated with water, thus grounding all of the utility poles and greatly reducing the amount of static electricity that is radiated into the air from the transformers and/or lines.


Grounding

G rounding is essential in helping to protect your sensitive electronics from damaging static electricity caused by lightning strikes. Although properly grounding your system cannot guarantee that at some point in time that your electronics won't be damaged by a lightning strike, it greatly reduces the potential and severity of a possible strike.

Grounding also can make a difference in helping to reduce EMI received from a nearby utility pole or bad transformer. But even when the system has been fully grounded and meets the National Electric Code on grounding TV reception equipment there is no guarantee that this will completely eliminate the interference. Still, you should make sure that the system meets the N.E.C. on grounding TV antenna systems and satellite antenna systems.
Electrical Service Meter
Electrical Service Meter

To do this, all coaxial cables needs to be spliced with a coaxial cable ground block as close to the point of entry into the building as possible. This ground block is then connected to with a #10 copper ground wire and a coaxial cable ground block to the building's electrical ground rod, usually found just below the electrical service meter. Also, the actual mounting structure of the TV antenna also needs to be grounded to this same grounding point.

By doing these two things, this keeps drains off nearly all of the static electricity that can build up during a thunderstorm and potentially damage the sensitive electronics connected to the system. Also, by having only one grounding point all grounds at the same potential and eliminates two different grounds that could potentially act as a highway for static electricity currents.


Filters

A s far as I know, there aren't any type of filters to completely eliminate EMI, but some high quality surge protectors, such as the one's made by Panamax, can remove some EMI. Cable companies have spent countless hours and thousands if not millions of dollars collectively to get rid of electromagnetic interference on their systems over the years. Many larger cable companies today have fiber optic cables that run directly from the TV stations to their "headend" instead of receiving the broadcasted off-air signal from the station's transmitter, totally eliminating any signal imperfections between the TV station's transmitter and their equipment.


Finding The Source

E MI interference can only come from one of two places, either inside or outside.

Indoor Interference

Sometimes appliances can cause offending interference. To see if the interference is coming from inside your house or not, try shutting off circuit breakers in your house while someone is watching the picture on the TV. If the interference is coming from inside of your house, you will know it as soon as you turn off the circuit that the offending source is plugged into. Some of the appliances that have a history of causing interference on TV's are electric blankets, popcorn poppers, microwave ovens, electric dryers, electric water heaters, or other types of motors where a spark is involved that can generate interference.

Outdoor Interference

When searching for EMI interference outside your house, an AM radio is an excellent tool for locating the source. Try walking or even driving around your neighborhood with an AM radio tuned to an unused frequency to pinpoint down the source for the interference. If you find that the offending interference on your TV is coming from outside the house, have the power company come out when you are home and show them the problem on your TV(s) and what you found out when you walked around with the AM radio. It may be that they have an old transformer on a nearby pole that is "spraying" the interference all over the neighborhood and causing interference on not only your TV's, but your neighbors as well.

As a last resort, you may want to move your TV antenna to a location that is farther away from the nearby power lines or even try using a more directive TV antenna where the reception angle in which it receives is more narrow, and thereby focusing in on the desired signal and rejecting any unwanted signals, ghosts, or interference.


For more information on all types of interference that can affect reception using a TV antenna system, visit the FCC's Interference Handbook.


If you have additional questions related to electromagnetic interference, feel free to contact us and we would be happy to assist you.


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