Video of a DCF77 receiver and a PWM generator with ATtiny25
If the following video does not display automatically: here
you can download it (123 MB).
The video starts with adjusting the receiver to the DCF77 frequency at 77.5 kHz.
The DCF77 signal strength reaches stage five on the display. Each second, the signal
goes down to below four.
Then I increase the receiver's frequency. DCF77 disappears and the typical long
wave noise increases. Until at a frequency of approximately 96 kHz: here,
the third harmonic of the 31.25-kHz-PWM generator can be seen. The harmonic also
reaches full signal strength.
Beyond that, a local carrier at 129 kHz can be seen.
On the second harmonic of the PWM generator at 61 kHz no signal can be identified.
Unfortunately I can't tune the receiver to the ground wave at 31.25 kHz, because
the switchable capacitors of the receiver do not provide this frequency.