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

Bob Smither smither at c-c-i.com
Fri Dec 9 15:52:39 EST 2011


Bob Smither wrote:
> 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).

I rebuilt my FE-5680A setup with new power supplies and better routing of the 
10MHz output.

BTW - I noticed that mine has a 1PPS output (~1usec positive +5V pulse) on pin 6 
of the DB9 connector.

The results are much more consistent with the new setup.  I have a 1PPS that is 
derived from the FE-5680A (not the native 1PPS output on pin 6) that is compared 
to the 1 PPS from a GPS receiver.  The first 15 hours of data can be seen here:

   http://c-c-i.com/node/154

 From the data, it looks like my FE-5680A is running about 1.7E-10 fast.  The 
data sheet specifies aging of < 2E-9/year so this seems reasonable.

I have been able to talk to it through the RS-232 port (pin 9 is output from 
FE-5680A, pin 8 is input to FE-5680A).  Using Cutecom on Linux with 9600 8N1 
results in the following dialog:

   2d 04 00 29 <- input command - request frequency offset
   2d 09 00 24 00 00 00 00 00 - reply

 From the reply I am assuming that my unit has no programmed offset (32 bits of 
zeros - last hex digit is the data checksum).

My documentation states that the full range of adjustment is:

   7f ff ff ff => +383 Hz
   80 00 00 00 => -383 Hz

To correct the 1.7E-10 offset I need to slow it down by .0017 Hz or a count of 
-9532.

After this unit runs for 24 hours I will try to program in the correction.

More later ...

-- 
Bob Smither, PhD                                   Circuit Concepts, Inc.
=========================================================================
The American Republic will endure, until politicians realize they can
bribe the people with their own money.
         -- Alexis de Tocqueville
=========================================================================
Smither at C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)
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