Confusion about AM Radio Receiver

I am confused by the design of this AM receiver and tuner circuit.



I don't understand how the inductor and capacitors on the left design a circuit that resonates at a certain frequency, and I also don't understand why the resistor and capacitor in parallel after the diode create a low-pass filter.

Can anyone help me to understand this circuit?

 

umm image?
post the image, not a link to it.

 

Updated my post. My apologies for the inconvenience!

 

any parallel or series LC circuit is oscillatory circuit.
there are differences between the two, for example parallel circuit has high impedance at resonant frequency. antenna picks everything and sends to your radio. LC circuit eliminates any frequency except the resonant one (lower frequencies are shorted to ground through L, higher frequencies are shorted to ground through C, only right frequency matching LC circuit is not shorted to ground and can be passed through envelope detector.
note that this radio has no amplifier so only local station (strong signal) can be received with this device. for envelope detector to work, we need signal that has amplitude greater than Vf of the diode. Germanium diodes have smaller Vf so they are referred in circuit with no amplification.

series LC circuit works the opposite way it is short at resonant frequency.

circuit you posted is basic crystal detector where input stage is parallel LC circuit. as explained before tuned LC circuit picks station of interest, signal (if sufficiently strong) passes through the diode (only one halfperiod, the other is removed by diode).
this charges capacitor on the right side (220pF) when diode is conducting, otherwise charge from capacitor is drained through resistor. by selecting correct RC combination, we can remove high frequency component and smooth (average out) the signal so that corresponds to audio signal at radio station.

actually that 220pF is too small for normal commercial AM, should be 4-5 times larger value but since we are talking about audio signal and humans cannot hear high frequencies, this means it would work even without the capacitor. our ears would do the filtering (headphones too).

 

image here shows signal before and after diode.
notice how smooth output signal seam to be (last graph):
http://4.bp.blogspot.com/_BFZ2BmeJg...Block+diagram+of+a+detector+for+AM+signal.bmp

in reality you get something like top waveform. the amount of ripple on top of signal is result of selection of RC values for low pass filter after detector diode. ideally this would look like bottom trace: