[islandlabs] Low Pass Filter for the $5 Transmitter

Burns, William burns at cshl.edu
Fri Aug 27 13:49:08 EDT 2010


Jonathan:

You've got it right re: why a capacitor's impedance decreases with frequency.
The area under the curve of a single half-wave determines how much of a charge gets transferred to the capacitor, and the voltage/back_bressure that is seen from the capacitor is proportional to that charge.

So.. Shorter wavelengths have a smaller area under the curve, (a.k.a. a shorter charging time for the capacitor) so there's less charge on the capacitor to resisto the flow of the signal.

A longer frequency would fill the capacitor more completely, and result in a greater resistance to the further flow of current/signal.

-Bill

Is it incorrect? I was trying to look at _why_ the impedance increases - something along the lines of building up a charge on one side of the plates over a longer time (low frequency) works, whereas a short time on either side means no appreciable voltage.
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