[time-nuts] Ebay FE-5680A Rb: Are they that good?

Bob Smither smither at c-c-i.com
Thu Dec 8 15:04:51 EST 2011

Chuck Forsberg WA7KGX N2469R wrote:
> The price seems reasonable, esp. with free shipping.
> Does anyone have experience with these?
> Is the circuit board included?

I could not resist at < $40.00 delivered.  Mine has been running for a couple of 
weeks, but my measurements have been inconclusive (I suspect my setup is far 
from ideal, especially the handling of the 10 MHz signal).

The unit I bought was mounted on a sheared off portion of a large PCB with a 
ground plane / heat sink.  It came with an extra DB9 connector and another 
oscillator (Vectron, ~ 64MHz) thrown in.

I have not had time to see if my unit responds to programming from through 
RS-232, but there is connectivity through the pins and there is a MAXIM RS-232 
chip inside so I am optimistic.

When I first fired it up I simply compared its 10 MHz to a 10MHz OCXO that is 
(manually) disciplined to GPS (another project!).  I was impressed when after it 
locked and settled for a few minutes the two 10MHz waveforms were stationary. 
After a few minutes I could detect some slight drift, but I estimate the two 
sources agreed to maybe 2 - 3 * 10^-11.  That is about as good as I can keep my 
OCXO so I'm not sure which of the two sources is better.

The unit is now mounted on a large heat sink (from a surplus 100W RF load).  In 
my lab the temperature at the top of the case has been running around 45 to 50 C.

I am redoing my test setup as I write.  I have new power supplies and plan on 
routing the 10MHz better.

My basic test will be to track the (averaged) time interval between a 1PPS from 
an old Ref Tek 111A GPS clock and a 1PPS derived from the 5680A 10MHz.

After I have a few days of reasonable results I will report to the list.

Best regards,
Bob Smither, PhD                                   Circuit Concepts, Inc.

                America - born free, taxed to death ...

Smither at C-C-I.Com         http://www.C-C-I.Com       281-331-2744(office)
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