# Antenna to receive 50Hz

The human body seems to be a good antenna to pick up 50Hz, at least touching a scope's probe shows a 50Hz waveform more than a volt in amplitude. Is it possible to construct an electronic antenna that does the same thing? (Wavelength at 50Hz is 6000km)
And if there's so much energy in it (1V in 1M$\Omega$ is 1$\mu$W), then why don't high-impedance pins pick this up?

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## 2 Answers

A human body is a really crappy antenna at 50 Hz. What you are seeing is capacitive pickup, nothing like a antenna picking up a self-propagating wave.

Yes, any hunk of conductive material the size of a human body will pick up 50 Hz about the same. Since it's all capacitive coupling, its the area that matters, not the bulk. A proper size sheet of aluminum foil would do just as well, probably better. Just about anything large and metal will pick up 50 Hz, assuming this is coming from your power line and this is indoors where power lines are all around in the walls, cords running to appliances, etc. A metal desk that is not connected to ground is a good example.

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The body can couple large amounts of common mode voltage but little power. if touching a high impedance mic input, say humm. If poorly shielded, say hummmmm.

YOu can easily get 50~100V on a 10Mohm probe. THe reason the probe doesn't is that is shielded. As soon as you touch ground with another body part your probe will drop to zero V. Now can you say humm? Your best debug tool is your finger. With this you can inject power hum and DC offset to ground or whatever your other finger is connected to V+.. Measure your finger capacitance and resistance in various skin conditions, (dry or not). It is a useful bench debug tool, signal generator and ground capacitance. If that makes perfect sense, score accordingly. Generally good designs with adequate shielding and measured with a decent short ground clip are not too sensitive to stray fingers.

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"YOu can easily get 50~100V on a 10Mohm probe." Looking very sceptical ... –  stevenvh Apr 17 '12 at 14:10
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