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

EWKehren at aol.com EWKehren at aol.com
Sun Dec 11 19:25:06 EST 2011

Sorry I ever started this. In the past the FE5680's started out with a  
50.255 MHz XTAL, some time in the 2002 2003 timeframe they switched to 60 MHz  
using a DDS in the loop. All of these units can only be stepped in 7 E-13 
steps  limited by the resolution of the DDS. Having followed all the listings 
on this  subject is it safe to assume that 99% of the units sold in the $ 40 
range are  identical in that respect. At prior times there was and still is 
a unit  available that from the 50.255 drives a DDS and a programmable 
output is  available at a premium price. All seem to be above $ 100. Claims that 
the 60 MHz  units can be set in 1 E-13 is bogus and misleading. Maybe if 
you dither the  input, but since the loop is most likely digital I do not know 
what that will  do. 
Accept 7 E -13 or do as I will do, use the C field.
Pin 8 and 9 are RS 232.
Bert Kehren
In a message dated 12/11/2011 5:46:05 P.M. Eastern Standard Time,  
snappa09 at gmail.com writes:

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
Many of them advertise these connections:-

PIN  1:  INPUT +15V to +18V
PIN 3:  LOCK/UNLOCK  (high = unlock)
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  ?
All advice  appreciated.
time-nuts  mailing list -- time-nuts at febo.com
To unsubscribe, go to  
and follow the  instructions there.

More information about the time-nuts mailing list