Noob questions about antennas

Discussion in 'Wireless & RF Design' started by msr, Jul 19, 2009.

  1. msr

    Thread Starter Well-Known Member

    Jul 8, 2008

    I have some very noob questions about antennas for you.

    We have a high frequency sinusoidal voltage generator pluged into an antena. The antenna works because at high frequencies the displacement currents aren't neglegible right? Air is the dielectric and there's a current flow through it. Because of that a magnetic field is created, then a electric field and so on.
    So... there is current flowing in the antenna right?

    Is there any risk of touching an antenna, once it has current flowing through it and has a sinusoidal voltage generator at its input? From practice, I supose not, but why?

    Thanks for your help.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    It does not really matter about the exact wave shape - an excited antenna can cause burns or even death if the output power is high enough and you make contact with it. The output is measured in power - the antenna has voltage present as well.
  3. mauro.laurenti

    Active Member

    May 8, 2009

    Normally you do not burn because of the voltage and power generator attached of the Antenna.

    Also with high frequency you can use locally the Ohm's law V=Z I.
    Locally means considering your system made of little sum of RLC circuits (transmission lines). V, Z, I are functions of the time and space.

    So if you touch one point of the Antenna with your body you are the Z (some Kohm) to ground. Since normally the voltage we are talking about is few are safe.

    ...If you use a standard signal generator (normally sine wave generator) the voltage we are talking about is few volts so you don't have any risk...

    ...if you touch the Vatican's AM antenna in Rome...I think you will start smiling!
    ...before even touching the Antenna I think your hairs will also start dancing...or speaking...depending on what is on-air! :)


  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    A good resonant antenna with a relatively small power input will have extremely high voltages at the tips.

    A few watts into a straight quarter wave antenna mounted on a good ground plane is enough to cause contact burns if you lightly touch the very end. You will not feel these, the RF seems to kill the nerves at the same time - you just get a white, cooked, dead spot where you touched it and the pain comes later...
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008

    Yep...having worked around 100KW transmitters for a few decades, I've gotten some NASTY R.F. burns...Smelly too!

    R.F. burns are seldom fatal, but you can burn off some of your favorite appendages.