# FCCH

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**FCCH** stands for Frequency Correction Channel. It is a downlink-only control channel in the [GSM](/source/GSM) [Um air interface](/source/Um_air_interface). The FCCH burst, defined in GSM 05.02 section 5.2.4, is an all-zero sequence that produces a fixed tone in the [GMSK](/source/GMSK) modulator output. This tone enables the Mobile to lock its local oscillator to the BS clock as required in GSM specification 05.01 section 6. The FCCH is transmitted in frames immediately before the [SCH](/source/Synchronization_Channel).

## References

- 3GPP TS 05.01 Physical layer on the radio path; General description

- 3GPP TS 05.02 Multiplexing and Multiple Access on the Radio Path

- [http://www.3gpp.org/ftp/Specs/html-info/05-series.htm](http://www.3gpp.org/ftp/Specs/html-info/05-series.htm)

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Adapted from the Wikipedia article [FCCH](https://en.wikipedia.org/wiki/FCCH) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/FCCH?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.