1. Dec 10, 2007

### A.I.

I'm trying to somehow wrap my mind around how a simple radio works, but I've run into some problems at the tank circuit, what it does, and how it works.
The various resources I've tried to get answers from don't seem to be able to discuss this part of a radio without introducing numerous mathematical equations for capacitance and indictance, so I was wondering if anyone could explain, in layman's terms, how a tank circuit works in the context of a radio?

2. Dec 10, 2007

### LURCH

Basically, a tank circuit is a capacitor and an inductor in parllel. Somewhere before signal reaches the tank circuit, there will be a path for it to take to the amp. After the tank, there is a path to ground. So here's how and why;

the antena of the radio is getting hit with EM waves of all differing frequencies. These waves amount to an EM field moving across the antena. this movement of an EM field across a conductor induces, as you would expect, a voltage. The frquency of the voltage depends on the frequency of the wave moving across the antena. Since the antenna is being hti with all freqs, it sends signals at all different freqs into the tank circuit. For low frequencies, the capacitor in the tank is a path of very little "resistance" (actually capacitive impedence, but it amounts to the same thing), so low-frequency signal passes easily through the tank circuit to ground. Now, how low is "low frequency" depends on the value of the cap.

Conversely, the inductor is a low-impedence path for high freqs. Again, how high is a question of the value of the inductor.

So, if you select a cap that lets through all the low-freq signals (up to a certain freq), and an inductor that lets through all the high freqs (down to a certain freq), then you can select what freqs you send to the amp. You see, the lower limit for the inductor and the upper limit for the cap overlap. Any frequency in that overlap will encounter strong impedence trying to go throught that tank to ground. These frequencies will go to the amp, which has less resistance than the impedence of the cap or inductor. All other frequencies will see either the inductor or the cap as a path of less resistance than the amp.

3. Dec 10, 2007

### A.I.

So overall, the capacitor and the inductor provide resistance to a particular frequency, that in turn goes to the amp because there's less resistance, whereas the other frequencies find the least resistance going into ... whatever is grounding the system?
That's amazing! Who thought of that?

Thanks a lot for your help!