Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Making a TV Antenna smaller

  1. Jun 10, 2010 #1
    According to this website for building an antenna the optimal length of the rods is 7 inches. Can I take 7 inches of copper cable and wrap it around a ferrite core to make a smaller version of the antenna that is just as effective?

  2. jcsd
  3. Jun 11, 2010 #2


    User Avatar
    Science Advisor
    Gold Member

    No. The length of the rods is taken in regards to the wavelength of the signal you wish to recieve. The physical size of the antenna is designed so that it will be resonant with the desired frequencies. Deviation from these dimensions will adversely affect the efficiency of your antenna. In addition, changing the physical shape of the antenna will also diminish its performance. For the most part, these "HDTV" antennas are nothing special and may even reduce your reception. The basic TV antenna is already designed to be resonant with your TV signals. However, it is designed to accept signals from all direction. Most people live in places where most of the signals come from one direction (say the major metropolitan area) and thus you can improve your reception by getting an antenna that is highly directive that focuses its reception along a smaller sector of the sky. So by changing the shape of your antenna you would be impacting the ability for the antenna to be highly directive and thus removing any performance gains you might see.
  4. Jun 11, 2010 #3
    Ok, I guess thats why manufactures have not done it :)

    Side question..

    Is there a minimum thickness required of the rods required, or is length the only thing that matters?
  5. Jun 11, 2010 #4
    Well this isn't entirely true. If the antenna is a printed circuit on a high dielectric substrate such as alumina, the lengths of the elements (rods) can be reduced to approximately 1/3.
  6. Jun 11, 2010 #5
    That is not a whole lot. I was thinking on the order of a radio, which usually has a 2 mile antenna inside of it.

    Now that I think about it every radio I have ever had has crappy audio quality though.
  7. Jun 11, 2010 #6
    Tell us what size you would like to make the antenna and we'll tell you whether it's possible or not and if possible, what's the best way to go about it. Do you need to pick up signals in only one direction or from many directions? Is yours for HDTV too, or for some other use? What are you using now and why is it unsatisfactory?

    In general the size of the antenna depends on the wavelength of the frequency you're trying to receive. The reason AM radio antennas have so much wire is that the wavelength of the signal is so long. The higher the frequency, the smaller the antenna. Also the more gain you want in the antenna the more elements you need and the bigger it will be.

    The audio quality of a radio is more dependent on the speakers than on the antenna.
  8. Jun 12, 2010 #7
    What about fractal antennas?
    Don't they reduce the size by using "bent" elements that are close in overall length to the staight element?
  9. Jun 12, 2010 #8


    User Avatar

    Staff: Mentor

    And if you're going to use it for TV or AM or FM radio, how far are you from the stations, how strong are they, are there terrain factors like mountains involved?

    If you're in the USA or maybe Canada, a useful site for getting information about TV signals at your location is TV Fool, and for FM radio, the similar FM Fool.

    You can find a lot of information about TV antennas at


    Note particularly the section Common TV antenna types.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook