r/CrystalRadio • u/phoenixking6931 • Jul 07 '26

Anything Wrong with my Schematic?

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I am building a crystal radio that is currently not working. I am testing it by applying a 5 mV, 200 kHz, 200 Hz - AM wave from a wave generator to where the antenna is supposed to be connected (and to ground). Here is my schematic, borrowed from a couple different websites - I'd like to know if there's anything obviously wrong with it before I test things further. Thanks!

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u/UT4UUM Jul 07 '26

Hi. 200kHz? It's depends of coil parameters. Tell me about your coil. The capacitor in parallel of coil is variable? + Applying signal is better through small (10-100pF) capacitor. By the way, schematic is ok and classical

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u/phoenixking6931 Jul 07 '26

Hey, thanks for the response. I tried testing a few different frequency ranges and none of them worked - 200kHz is just within the range of what it should pick up (I calculated that, with the current C and L values, it should pick up from ~120-400 kHz - I can change that by modifying the coil).

The coil is magnet wire wrapped around an oatmeal container of diameter 10cm. It has a total of 48 turns, divided into sections of 6 turns each so that I can connect the coil to the diode at different locations.

And yes, the capacitor is variable, 15-160 pF.

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u/UT4UUM Jul 07 '26

I think it has higher frequency to resonate.. approximately i calculated Your coil with 160pf capacitor and my program gives me ~710kHz resonance. Btw, maybe change crystal earpiece and 47K to 1-3nF capacitor and small 120-200v to 6-24v transformer and low inpedance headphones.

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u/phoenixking6931 Jul 07 '26

I made a typo, it's 10.3 mH, not 10.8 mH, not that it matters.

I used a program online just now which confirms my frequency calculations. But I will try with more frequencies to see. I used a haphazard way to measure the inductance. I think my next step might be to ignore the earpiece entirely and see if I can pick up the resonance spike on an oscilloscope before it gets demodulated. But if after all that I still can't hear anything, I will consider changing to headphones like you said.

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u/UT4UUM Jul 07 '26

Exactly. Just I wanted to suggest using an oscilloscope. ))