[time-nuts] FE-5680A GPSDO controller also works with FE-5650A

[Skip Withrow]

Hello Time-Nuts,

Nick Sayer's GPSDO controller will also work with the FEI FE-5650A rubidium
oscillators as well.  A small modification is needed to the board, but is
rather trivial.

First, the 5680 outputs 10MHz on pin-7 of the DB-9, the 5650 has a separate
SMA connector.  So, pin-7 needs to be lifted from the GPSDO board (the 5650
has the VCXO monitor on that pin).  And a short coaxial pigtail needs to be
run to ground and the GPSDO 10MHz input (I soldered the center conductor to
the chip cap on the top of the board.  I also just use an SMA coaxial Tee
to run the 10MHz to my monitoring equipment.

Second, the 5680 has an RS-232 interface and the 5650 is TTL.  So, the 5650
can be modified for RS-232 (the pads are in the unit, the RS232 chip and 5
caps must be added), or the RS-232 converter can be taken off Nick's board
and two small jumpers added.  I have done both.

I have asked Nick to add changes on the next pass of the board to
accommodate these changes more easily.

These mods assume a 5650 that RDR-Electronics has modified to have the same
control word resolution as the 5680.

I hope to publish some Lady Heather plots soon of the GPSDO performance.
One nice feature is that Nick's code is open source and if people wanted to
add features (such as the EEPROM write) it should be easy to do.

I know I have had fun playing with the controller the last couple of seeks.

Regards,
Skip Withrow

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