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Old 27th Sep 2018, 3:29 pm   #12
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
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Default Re: FM to AM converter - variation on a theme!

Thanks Lawrence and Derek for your helpful feedback.

Derek has also clarified the point that you made Lawrence and I've modified the sketch accordingly. Given the consumption of the FM module it clearly makes more sense to power the converter from a 'wall wart' rather than batteries. Hence, I've shown a concentric power socket, and have also added a reverse Voltage protection diode as a precaution in case a wall wart which has the centre-pin negative gets inadvertently plugged in, but the diode could be omitted if felt unnecessary.

Hopefully, the circuit now looks OK.

Derek has made the point that he only changed C4 & C5 from 220pF to 150pF to move the AM frequency higher up the MW band away from an interfering station.
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