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kahlenberg
Antenna-Theory.com Newbie
Joined: 14 Aug 2013
Posts: 1
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 Posted: Wed Aug 14, 2013 4:01 pm Post subject: From which frequency does the radiation begin? |
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Hi guys,
I have a question as subject already says: From which frequency does the radiation begin?
Theoratically, can we build a 1Hz or 50Hz-60Hz transmitter and receiver?
Is there any low frequency limit to be radiated?
Is there any relationship between this limit (if any) and free space impedance 377 Ohm?
Thanks. |
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bigSteve
Antenna Wizard
Joined: 14 Mar 2009
Posts: 265
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| Posted: Wed Aug 14, 2013 5:48 pm Post subject: Radiation and Intrinsic Impedance |
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No: there are no limits. However, when you get to 1 Hz (for instance), effective radiation requires a sizable fraction of a wavlength for good radiation efficiency. Note that a half wavelength at 1 Hz about 15,000 km - which means you would need an antenna about the size of the Earth.
You cannot radiate D.C. (0 Hz) waves, as there will be no interaction of magnetic and electric field for propagation.
This all has absolutely nothing to do with the 377 Ohms characteristic impedance of free space, which is frequency independent.
Links:
http://www.antenna-theory.com/definitions/intrinsicimpedance.php
http://www.maxwells-equations.com |
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