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Old September 8th 08, 08:55 AM posted to rec.radio.amateur.antenna
Sal M. Onella Sal M. Onella is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 442
Default Quick Rooftop Antenna For Channel 2?


"JoeSch" wrote in message
...
I apologize for making this about TV reception instead of radio, but I
did not know where to turn.

I live in Connecticut, about 100 miles from New York City, (102 miles
by the lattitude-longitude charts) and I am about a block from the
water, Long Island Sound.

I grew up in New York and am a NY Jets and Giants fan, which is
broadcast from the Empire State building. The Giants' games are
carried by one network, but the other Connecticut stations only carry
Patriots games, not the Jets.

The Jets' games are carried on channel 2 New York, which is 102 miles
as the crow flies from my house. Football packages on satellite TV
are beyond present financial condition. I only care about channel 2,
New York.

Does anyone have any ideas for a quick rooftop antenna I can put on a
pole and run into my house for the Jets game? I really don't mind if
the signal is somewhat snowy as long as I can make out what is
happening on the field-beats radio. Besides, this is football-
sometimes it snows for real and nobody complains, lol.

Anyway, any help would be greatly appreciated.

PS: I have seen websites for dipole antennas. My second question
is: If I make a dipole antenna, what if I mounted it on a piece of
cardboard or styrofoam for it's length, which cardboard or styrofoam
has aluminum foil on the reverse side? The aluminum foil would not
contact the dipole, and be separated from it by one quarter to one
inch, depending on material thickness. The reason I ask is if this
will cut off 180 degrees of reception, thereby improving the signal to
noise ratio, (I know a little about electronics as an audio hobbyist,
but very little about antennas even though I have tried to get a
grasp).


First of all, don't introduce any other metallic objects (foil, etc). Just
the elements described below.

You need to make a basic yagi antenna. When finished, it greatly resembles
a TV antenna, except the elements are all nearly the same size, optimized
for Channel 2. (Neglecting the fact that WCBS digital TV is on a UHF
channel. You asked for analog WCBS-TV, Channel 2.)

Fabricate a folded dipole for 57 MHz out of regular TV twinlead.
He http://www.wfu.edu/~matthews/misc/dipole.html
Looks like he uses Channel 2 as an example -- convenient! He says it's 2.5
meters long -- I think that's about 98.4 inches

Probably should mount it on an 8-foot piece of 1 X 2 wood to keep it
straight and level. An inch or so will stick out at the ends -- no big
deal. It will go on the roof, mounted crossways on another piece of wood
called a "boom" which is aligned to New York City. The folded dipole's
position on the boom should be about 2 feet from the end that will be away
from New York.

That is the active or "driven" element of the yagi and it needs some
helpers. The helpers are made of ordinary metal tubes, but have no direct
electrical connection to the driven element. Old aluminum tubing is fine.
Assorted pieces of old TV antennas will work if the pieces are tightly
fastened together and carefully cleaned at the attaching points for a good
connection.

One helper is called a "reflector" Make it 6 percent longer than the driven
element and mount it on the boom behind the driven element (away from New
York) by about 21 inches.

Next helper is called "Director #1." It's 1% shorter than the driven
element and it's mounted on the boom 21 inches in front of the driven
element, toward New York.

Next helper is called "Director #2." It's 8% shorter than the driven
element and it's mounted 37 inches in front of Director #1.

You can add more directors, same length, same spacing as #2, but they won't
capture a lot more signal after the first few. Plus, with more than two
directors, the boom gets really, really long.

Note that this antenna is a 300-ohm antenna. Since your TV input is probab
ly NOT 300 ohms, you have to transform the impedance to the 75-ohm coaxial
cable that plugs into the TV. Do that near your antenna. What I mean is
this: Have only about a foot or so of 300 ohm twinlead coming down from the
folded dipole. Connect a 300/75 ohm transformer or "balun" at that point
and run coaxial cable the rest of the way to the TV. Much better for
interference rejection, especially at Channel 2. Such 300/75 ohm baluns are
available at all radio stores as well as many variety, drug and department
stores. Buy whatever one you think you can connect with the tools at hand.
You may have a balun or two that came with an old TV or VCR.

The first one of these I ever helped build was made with coathangers on a
broomstick for Channel 13. (Higher freq meant smaller elements -- easier.)
It worked fine.

Let us know how this works for you. I'm interested to know if you were able
to follow what I wrote.