Electronics > Beginners
Analog bandpass filter - bode plot for various filter types
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ogden:
Yes, oldskool approach is impractical. I would suggest Tayloe mixer (detector) + SDR approach. Much more fun definitely.

Here you can taste (hear) how one of simplest DIY Software Defined Radio works: http://hackgreensdr.org:8901/

Quite detailed description of hardware: http://hackgreensdr.org:8901/bunker-system.pdf

DCF77 is so slow that you can do all the DSP on Arduino and have spare CPU time left.
petert:
Thanks for all that great info. I'll need time to process all of it.

SDR is definitely a route I want to go (I recorded the DCF77 radio signal using a soundcard before, and processing in software is no problem).
But this is a project to learn more about analog electronics, so I want to stick with it.

I saw that crystal oscillators can be used as resonating filter with a very narrow bandwidth. A pierce oscillator seems reasonably simple.
http://thehackerworkshop.com/?p=364
https://www.mikrocontroller.net/topic/78005 (German, but useful info on crystal oscillators).

PCB of a crystal filter with soldered BNC jacks: http://www.philipstorr.id.au/radio/technical/Crystals%20Techo.pdf

Test a crystal and tune a pierce oscillator: https://www.electronicdesign.com/test-measurement/simple-tester-provides-readout-crystal-frequency

A crystal oscillator circuit with completely specified parts and values: http://www.z80.info/uexosc.htm

I didn't find a calculator for such a pierce oscillator, any idea?
ogden:

--- Quote from: petert on September 24, 2018, 02:45:09 pm ---But this is a project to learn more about analog electronics, so I want to stick with it.

I saw that crystal oscillators can be used as resonating filter with a very narrow bandwidth.

--- End quote ---

Do not try to build 77.5KHz carrier detector with needle-sharp bandpass filter. Learn heterodyne receivers instead - it's still analog electronics.
petert:
Regarding impedance matching, I'll add a good video here for (future) reference:

Measuring output impedance:
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