Tell me more ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.
up vote 1 down vote favorite

I have been reading about how a crystal radio works and I have one question below:

enter image description here

It says, the energy in form electric current from a specific frequency will be stored in the coil (or a resonator) and all the other voltage will pass through the ground. How does it let it pass through the coil while storing the other voltage from frequency we want? How does the frequency capturing exactly works here?

share|improve this question

2 Answers

up vote 1 down vote

It's exactly the same circuit as your other question What makes up a resonator of radio? but here the capacitor is the wire in the antennea. By changing where along the coil you complete the circuit changes the amount of inductance used and so the frequency of the LC resonator

share|improve this answer
I still don't get why does the coil store only a specific voltage from some specific frequency. Does it depend on the length of coil, i.e. length is proportional to voltage? Therefore, It can be assumed that different frequencies produce different voltages, – Ryan Jan 19 '12 at 6:57
Ryan, it does not store it. As the carrier wave comes it goes to a diode crystal which turns the modulation of the amplitude into sound, continuously. Have a look at "how it works" in the wiki article en.wikipedia.org/wiki/Crystal_radio . – anna v Jan 19 '12 at 7:25
up vote 1 down vote

Actually the capacitance in this case (What makes up a resonator of radio? ) is the winding capacitance of the mutual coupled, tapped inductor. What the wiper arm does is shunt out, bypass the lower section removing the AM carrier (rectifier LP filter).

The capacitance of the antenna wire, even say 100', is well short of a pF although it does exist.

share|improve this answer

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.