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

Nick Sayer nsayer at kfu.com
Mon May 23 16:20:15 EDT 2016


> On May 23, 2016, at 11:34 AM, Skip Withrow <skip.withrow at gmail.com> wrote:
> 
> 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.

Big, huge thanks to Skip for not only recovering the 5680 that my early firmware bricked (that has not recurred, by the way, so I have some hope it’s all better now), but for being an independent tester of the prototype.

The revision of the board that’s on the way back to me has an error and the RS-232/TTL jumpers are, unfortunately, worthless. To do the TTL conversion for that version you have to pull the chip off, but as long as the first 3 customers have 5680s, it won’t matter to them. Once I verify there are no other errors (I expect there are none), I’ll order a larger run with that error corrected.

The third jumper, however, does work properly and allows you to reroute the RF input from pin 7 to an on-board U.FL connector footprint. You can either add the U.FL SMT jack or just solder on to the center pad, and then swap around the two-way jumper. This is useful for other FEI oscillators like Skip’s modified 5650s, or 5680s that have SMA output jacks.

This version also has an improved power supply compared to what Skip’s been using. I’ve been seeing improved results. Surprisingly (to me), it’s been improvements on the 5v rail rather than the 15v rail that have been the most beneficial.




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