A personal project to generate a local DCF77-compatible signal for radio-controlled clocks at home.
I live in Slovenia, far from Frankfurt, so my clocks rarely receive the original DCF77 broadcast reliably.
This project solves that by retransmitting a local signal indoors.
DCF77 reception can be unreliable in my location. Instead of constantly resyncing clocks manually, I built a small local transmitter that gives all clocks in the house a strong, stable signal.
This repository contains two transmitter approaches:
- Software-triggered RF
- Hardware-generated RF using a Si5351A daughter board module from AliExpress
I started with the software implementation first because I was impatient and did not want to wait for shipping.
- Initial build:
- It worked, but timing jitter was visible:
- Despite the jitter, it successfully synchronized a clock:
- Module used:
- Trigger quality improved:
- RF signal quality improved as well:
Final tuning required moving the primary and secondary coils for optimum resonance and power transfer.
- Final tuning was done by observing the induced signal in a nearby DCF77 receiver coil:
- Best coupling happened when both primary and secondary coils were near the end of the ferrite rod.
- Final practical challenge was finding one orientation that worked for all four clocks in the house.
- The final unit now runs from a cupboard:
- This is a local, experimental low-power setup intended for private indoor use.
- The project is focused on practical reliability rather than laboratory-grade instrumentation.
This project is intended for private, low-power experimentation in a controlled local environment. Radio transmission rules vary by country. Before building or operating a DCF77-like transmitter, check and follow your local telecom/radio regulations.
Working and deployed at home, supports:
- Over-the-Air (OTA) firmware upgrades,
- Transmits 4 times per day for 20 minutes (around 01h00, 02h00, 03h00 and 04h00).
- A tiny web server listens for manual trigger requests..