MHz reference option -
External 10 MHz reference option
This option is not part of the standard build. However, it is possible
to operate the board from an external 10 MHz reference source. If the
following components are fitted, the on-board TCXO can be made to
switch off automatically when the external source is fitted. For this
to work, the external source must present a low (less than 1k) dc
resistance to ground.
*The value of R25 may have to be increased if too great an input signal
from the external reference is present (or attenuators added to ext
Nominal input: 0 – 5 dBm
It is important to ensure that R1 (0R), which is part of the ‘standard’
build is removed.
These components are shown towards the top left hand corner in the
following picture (see also the layout drawing at the beginning of this