Use OsmocomBB as OpenBTS / airprobe clock generator

Harald Welte laforge at
Sat Apr 10 21:47:45 UTC 2010


Recently we've had the idea of using OsmocomBB with a simple firmware
that synchronizes to an existing GSM networks FCCH and use the resulting
13MHz clock to drive the USRP for airprobe or OpenBTS.

Ideally, we would even use the Calypso-internal PLL (for ARM or DSP) to
multiply it up to the required 52 MHz.  However, neither the Openmoko
nor the Compal/Motorola phones expose any of the 3 clock output pads :(

So the only choice is to use something along the lines of the
as a quad clock multiplier and attach it to the CLK13OUT signal of the

The chip is available for 9 USD in single quantities at digikey, and
possibly cheaper at other sources.  Combined with a sub-20EUR phone it
might be a very cheap but still accurate frequency source for OpenBTS -
at least as long as there are any commercial gsm networks available.

- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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