[time-nuts] Ebay FE-5680A Rb: Connections and Features

Bob Smither smither at c-c-i.com
Sun Dec 11 18:00:54 EST 2011

alex mclaggan wrote:
> Like many of you, I have seen these advertised on Ebay at good prices.
> Also, like many of you, I am confused about the 'programmability' and
> connections.
> Many of them advertise these connections:-
> PIN 1:  INPUT +15V to +18V
> PIN 3:  LOCK/UNLOCK (high = unlock)
> PIN 4:  INPUT +5V
> PIN 7:  OUTPUT ( 10MHz sinewave )
> Many of them also say "Digitally programmable to 1x10-13", with the above
> connections.  (Many of the sites seem to have the same descriptive text.)
> On questioning one of them about how the programming was done, they replied
> "Not with this model; only with the more expensive one he sells !"
> But from what I read in some of the time-nuts contributions, there is
> sometimes (?) or often (?) also these connections:-
> Pin 6   1 pps out
> Pin 8   RS-232 Rx  (into rubidium)
> Pin 9   RS-232 Tx  (from rubidium)
> Can anyone tell me if they ALL have the MAX level shifter/driver chip
> fitted, even though it may not be connected to the connector ?  I don't
> want full programmability, just 10 MHz frequency correction. Perhaps I just
> have to take pot luck when I buy ?  What are my chances of getting one with
> the 'hidden' RS232 and 1PPS output ?

For what it is worth, this unit:


appears identical to the one I purchased four weeks ago.  Same seller, same cut 
off PCB, same "extras" thrown in, same price.

My unit has the pins and functions you list above (including the 1PPS and the 
rs-232 connections.

I have been able to adjust the frequency in a restricted range around the 
nominal 10MHz.  The results from my experiments can be seen here:


Bob S.

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