Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I have a gizmo that broadcasts an FM radio signal from my phone's headphone socket to my car's radio antenna.

Sometimes, there's another station on the same frequency with a stronger signal and my car plays that signal instead. However I've noticed that if I hold my hand up near the transmitter, my signal takes over again.

What's going on when this happens? Am I somehow boosting the signal with my hand?

share|improve this question
add comment

2 Answers

up vote 5 down vote accepted

You're not boosting the signal; you're either acting as a reflector (capturing a bit more of it to feed to the antenna) or blocking a competing source, or perhaps a bit of both.

By analogy, when you hold your hand to your ear to help you hear something, your hand is acting a reflector for sound waves to direct a little more energy into your ear. It can also keep out other extraneous sounds coming from other directions.

Our bodies contain a lot of water and other chemicals which makes them fairly electrically conductive. Any electrically conductive material can serve as either an antenna or a radio-reflective element. So, the position of your body relative to the radio antenna will affect its reception.

share|improve this answer
add comment

A human body may reflect and absorb radio frequencies, though not very efficiently. It may as well act as a resonance chamber for certain frequencies. For a signal of 100 MHz, the involved wavelength is 3 m, and so it is possible that parts of your body are acting slightly as a resonant chamber. (for an optimal resonance, you should have 1.5 m diameter, too many cheeseburgers...)

You might be surprised if you have a look at the amazing Lydia Kavina and other theremin players videos around. This instrument is played without any physical contact, by merely doing hand movements near the antennas. The human body acts itself as a part of an L-C circuit.

enter image description here

share|improve this answer
    
I cannot resist adding a couple of additional amazing links: another Lydia Kavina performance, and a curious amateur thereminist playing The Beatles in front of M51 –  Eduardo Guerras Valera May 11 '13 at 20:13
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.