Since firmware 2016.01-rc1 bladeRF has the ability to lock to an
external reference as well as produce arbitrary frequency signal
(25 MHz here) on its clock output.
Use gr-osmosdr source with the following arguments to produce 25
MHz on the SMB connector:
osmocom_fft -a bladerf,smb=25e6
smb=25e6
To lock the bladeRF itself to an external GPSDO reference, use
additional arguments tamer=external for 10MHz or tamer=external_1pps for
1PPS GPSDO signals.
osmocom_fft -a bladerf,smb=25e6,tamer=external
tamer={internal,external_1pps,external}
The described method requires https://github.com/Nuand/bladeRF/releases/
tag/2016.01-rc1
Carefully *read the instructions for external reference locking*
(especially max allowed voltage levels) on Nuand's blog https://
www.nuand.com/blog/2016-01-rc1-release/