From: SFPhysics@aol.com
Date: Thu Aug 31 2000 - 11:18:52 PDT
From: SFPhysics@aol.com Message-ID: <ba.a5f812d.26dffb8c@aol.com> Date: Thu, 31 Aug 2000 14:18:52 EDT Subject: Human Antenna !
> What is the physics behind the body as an antenna? Why do we sometimes get
better reception when we grab the antenna of a radio?
> I know we conduct better than the air and (most) walls around us, and that
the moisture and salts on our skin make a fairly good connection between us
and the antenna, but what is the rest of the physics of this phenomena? Is
it ONLY because the antenna is, in effect, made longer?
> Thanks,
> Ben Pittenger
> bpitt@n2.com
>>
Ben:
1) Both TV and FM signals are high enough in frequency to bounce off things
and give "multipath distortion" which is too many signals arriving at once
causing a reception problem (ghosts on TV and fuzzy sound on FM). The
internal circuitry of the radio or television has a circuit for adjusting the
amplitude of the incoming signal. When you add your body to the antenna and
the input signal is increased, the circuit adjusts for the strongest direct
signal and the lesser bounce signals which cause the problems are rejected to
some extent. In electronic terms it is called "capture ratio."
2) The human body is an antenna but it is also a wave absorber. The salt
and water make for a good electromagnetic wave sink. When you hold the
antenna you add some signal but you also subtract the signals that cannot go
through you to reach the antenna. Thus you subtract some of the lower signal
strength multipath reflections when you stand in the right position. In
effect you are aiming the antenna for a better signal. Without you the
normal cheap monopole antenna has a 360 degree pattern of reception
sensitivity.
3) The human body is also a wave reflector. To some smaller extent the
human body as an electrical conductor will reflect waves. Putting your body
near to an antenna helps the directionality of the antenna improve. You
become part of a dipole antenna and the reflector of a monopole antenna. The
reflection helps the antenna again to be more directional. Again this
improves the monopole directivity.
4) The capacitance of the human body to absorb or give off electrons allows
the body to electrically interact with the antenna and become an active
element in the reception process of the metal antenna picking up waves.
Thus, your body position can act as a tuner to augment or suppress parts of
the waves being received. I hope my explanations have been fairly clear.
Best wishes to you and the rest of the Pinhole Gang,
Al Sefl
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