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On 10/24/2013 02:15 PM, W5DXP wrote:
On Thursday, October 24, 2013 7:57:52 AM UTC-5, J.B. Wood wrote: On 10/24/2013 08:10 AM, W5DXP wrote: ... a human body should have the same effect on both antennas but we can demonstrate that it doesn't. No I'm sorry, but that is a non-answer. Please explain, within what you have been asserting, how a human body can have a completely different effect on two antennas that receive identical EM waves. -- 73, Cecil, w5dxp.com I would like to think this is an easy one: Say we have a receiving antenna such as a loop that isn't operating in the presence of nearby (close in coupling) objects such as metal, ferromagnetic cores, or human skin. If we introduce these objects, we see that compared to operation in their absence we have in general altered the antenna's gain, pattern and feedpoint impedance. IOW, the nearby structures are now part of the antenna. Suppose we setup a dipole antenna and a loop antenna of appropriate dimensions such that both are responding to the same E-M wave and produce the same available receive power at their feedpoints. Just to keep things simple, assume both antennas are low in resistive losses and they are operating free of nearby objects of the type I mentioned. Either antenna could produce the same power dissipated in an conjugately matched load at its feedpoint. If we now place objects near either antenna, anything goes, depending on the objects and how they're oriented with respect to either the loop or dipole. None of this, however, can be used to assert that the E field is favored/more responsive than the H field or vice-versa for a particular antenna structure. Sincerely, -- J. B. Wood e-mail: |
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