Re: How Can you Make a VHF TV Antenna for an Attic

Discussion in 'Electronic Repair' started by Sal M. Onella, Jul 15, 2009.

  1. <> wrote in message
    news:...
    > Hi - I need to receive VHF TV (channels 6,7,9,13) and would like to
    > make a super-duper antenna for inside my attic. I would have thought
    > that I could easily find (simple) instructions on the internet but
    > can't. Does anybody have a simple idea that just uses wire (wire
    > should be easy to attach in an attic).


    I'd like the answer to be YES, but it's NO.. If you wanted to make an
    antenna for just one channel, I'd say yes. I already did it for some guy
    who wanted a channel 2 antenna over a year ago.
    >
    > I've seen some instructions (mostly UHF or DTV) and some of them do
    > calculations for wavelength (let's say 5 feet).


    It's a multi-step process. You have to look up the channel frequency for a
    TV channel. Then, you take the number 300 and divide it by the frequency.
    The result is the wavelength. The elements are then cut for approximately a
    half-wavelength. More details below, if you want 'em.

    Multi-channel antennas have multiple elements, all differing lengths. If
    you have one element, you can expect to receive one channel well and other
    channels maybe but not as well. A single channel antenna can be made of TV
    twinlead and attached to a piece of wood. It's called a "folded dipole."
    More below.

    > And then, with no
    > explanation, the guy just says "I made it 10 feet for better
    > reception". So I ask, can I not then just use the entire length of my
    > attic for super-duper reception?


    Nope. He's full of it to say that. The only thing that gets longer to make
    a better antenna is the boom, the center long rod of a long antenna, and it
    gets longer because additional elements are added to it to improve the
    performance. However, you have to know how many, how long and where to put
    them. That's why we study this stuff.

    > Wire is cheap after all, and I only > want to crawl up there once.


    Crawl up there once and bring a TV antenna with you ... a STORE-BOUGHT TV
    antenna. Hang it flat from the rafters. A balun is a little matching
    transformer with side-by-side wire connections on one side and a round
    coaxial cable connection on the other side. Picture here:

    www.summitsource.com/images/products/COTRAN.jpg

    Most antennas have two screws for attaching one side of a balun. Connect
    your coaxial cable to the other side.

    > Also, I see instructions that say you should aim the antenna without
    > defining "aim". Do you align the wire in the direction of the
    > transmission antenna, or should the wire by perpendicular?


    The outline of many TV antennas, viewed from above or below, resembles the
    outline of an arrowhead. That's it. The smaller elements are on the end
    that's nearer to the TV station. The signal arrives perpendicular to the
    alignment of the elements.
    http://www.radioshack.com/pwr/content/05/72/2112695_31954_thumbnail.jpg is
    an antenna which illustrates the arrowhead concept. The stations are off to
    the right side in this picture. I have no idea whether the antenna in the
    picture is any good.

    If you make a single element antenna, you align it perpendicular with the
    arriving signal. These do work pretty well, by the way.
    http://www.wfu.edu/~matthews/misc/dipole.html has some step-by-step
    instructions for making a folded dipole with ordinary tools.

    One last thing: It's not beyond the realm of possibility to make one folded
    dipole attic antenna for Channel 6 and a second folded dipole attic antenna
    for Channel 9. The Channel 9 antenna just MIGHT also handle 7 and 13 if
    you're in a good reception area. You can cable both of them to the TV and
    switch between them.

    Sal
     
    Sal M. Onella, Jul 15, 2009
    #1
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  2. Sal M. Onella

    Rich Webb Guest

    On Tue, 14 Jul 2009 23:28:21 -0700, "Sal M. Onella"
    <> wrote:

    >

    [snippety snip some good info from Sal]

    Also, to the OP, if you're interested in playing with this some, even
    just to the point of seeing what some of the radiation/reception
    patterns look like (goes-out signal strength is the same pattern as the
    goes-in sensitivity, btw) hop over to http://home.ict.nl/~arivoors/ and
    d/l a copy of Arie's version of the 4nec2 antenna modeling software.

    There are example files that are similar to typical TV antennas, among
    others. You can get a list of channel assignments versus frequency on
    Wikipedia.

    --
    Rich Webb Norfolk, VA
     
    Rich Webb, Jul 15, 2009
    #2
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  3. Sal M. Onella

    Alan Douglas Guest

    >Hi - I need to receive VHF TV (channels 6,7,9,13) and would like to
    >make a super-duper antenna for inside my attic. I would have thought
    >that I could easily find (simple) instructions on the internet but
    >can't. Does anybody have a simple idea that just uses wire (wire
    >should be easy to attach in an attic).


    There was an article in Electronics World in December 1967 by Harold
    Pruett titled "Designs for Log-Periodic FM & TV antennas". He used two
    lengths of hookup wire, attached to a wooden frame in a zigzag
    pattern, and gives all the dimensions needed. I built one then and it
    has worked fine ever since, though now there's nothing to receive in
    this area so I've switched to a UHF-only antenna in the attic. I can
    mail you xeroxes of the article. I'm adouglas (at) gis.net.

    Alan
     
    Alan Douglas, Jul 18, 2009
    #3
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