MadSci Network: Engineering

Re: Does a TV antenna that connects to a wall outlet really work?

Date: Fri Sep 18 09:38:46 1998
Posted By: Steve Czarnecki, senior technical staff member, Lockheed Martin
Area of science: Engineering
ID: 905407263.Eg

It's just about impossible to predict how well one of these gadgets would 
work for you.  It is true that your house wiring acts as an antenna; any 
piece of wire will.  However, that does not mean that the house wiring is a 
GOOD antenna that provides a CLEAN signal.  What the device does is pass 
any TV signals picked up by the wiring to your TV or VCR while blocking the 
household AC current.  What the device will also do is pass along any 
interference ("static") carried on the wiring, as well.

WARNING: Under no circumstances should anyone attempt to directly connect 
their household electric wiring to the antenna terminals of a TV or VCR.  
Damage to your wiring, damage to the equipment, a fire, electric shock, or 
even death are the likely outcomes.   

The problem is that the configuration of the wiring in your house is 
unlikely to be a good antenna.  The lengths of the wires are not matched to 
the wavelengths of TV signals, and the directivity ("antenna pattern") is 
not controlled or controllable, and impedance of this "antenna" is poorly 
matched to free space.  This meaning some stations may come in OK while 
others don't come in at all or are subject to a great deal of ghosting and 
fading, and there's nothing you can do about it.

Also, any electric motors in your house (especially for small appliances), 
flourescent lights, and light dimmers are likely to generate interference  
that degrades the TV picture (streaks and "snow").  This electrical "noise" 
will is carried on the electric wiring and this device will pass it 
directly into your TV or VCR along with the desired signals.
I've seen this things advertised, but for the same amount of money, I'd 
simply go buy a pair of rabbit ears (that's what I use).  You can get 
fancier ones that include a signal amplifier, but a set in the $10-$20 
range with a "channel selection" knob will work about as well as a set of 
rabbit ears can work, assuming they're connected to anything other than the 
very cheapest TV or VCR.  This is because the amplifier in the tuner of 
even a moderate-quality TV or VCR is likely to be better (i.e., have lower 
noise figure) than the amplifier in a pair of rabbit ears.  

Steve Czarnecki

P.S. #1  I'm assuming you don't live in a building with metal walls or a 
metal skeleton (much commercial construction and an increasing amount of 
residential construction uses galvanized steel studs rather than wooden 
2-by-4 studs).  If you do live in a building with a metal wall or metal 
studs, only an outdoor antenna is likely to work well.  

P.S. #2 An alternative to mounting an antenna outside is to mount it in 
indoors (in the attic, for example), assuming you don't have metal walls, a 
"tin" roof, or metal studs in the walls.  In a wooden building, the antenna 
will work just fine indoors.  They're usually mounted outdoors simply to 
get the highest possible vantage and becuase they take a lot of space.

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