MadSci Network: Physics

Re: Re: why does my radio reception change if i stand near radio?

Date: Thu Nov 1 10:06:01 2007
Posted By: Madhu Siddalingaiah,
Area of science: Physics
ID: 1174759833.Ph

Hi Mark,

That's a good observation that you made.

In general, this is known as proximity effect. There are two possibilities:

1. Your body is shielding or attenuating some of the signal from the radio

2. Your body is detuning your receiving antenna

It's possibly both effects are taking place. I suspect this because you say
you live out in the country, in which case you might be far away from the
radio transmitter antenna so signal strength is weak. You also mentioned
that you use a cheap antenna which is most likely omnidirectional and
probably not very well tuned.

Radio waves, like visible light, contain both electric and magnetic fields.
Your body looks like a large bag of water to radio waves. Water acts as a
dielectric, meaning it concentrates electric fields. You might think of it
as a lens in visible light. As you move away, you are altering the strength
of the electric field in the radio waves, which you notice as varying
signal strength.

Mobile phones are also affected by the proximity of the human body. Mobile
phone manufacturers tune their antennas assuming a human body is close by.
Of course, they can't account for all possibly orientations, so they often
recommend not touching the antenna during operation as this can reduce it's

I hope that helps. -

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