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?
Answer
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.
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