[time-nuts] FEI 5680 Rubidium

Rex rexa at sonic.net
Tue Feb 8 19:35:27 EST 2005

On Tue, 11 Jan 2005 01:43:35 -0600, Brian Kirby <kirbybq at bellsouth.net>

>On Ebay, a seller has a FEI 5680 rubidium.  See 
>Has anybody seen any data/info on programming these units ?  Internet 
>search came up negative.
>Thanks - Brian N4FMN

I thought I would bump this question about FE 5860A rubidium sources

Brian and I both ordered one. When I tried mine it drew current on +15 V
that looked like an oven warming up, but never gave useful outputs. By
email, I found Brian had the same results. We both returned them for
exchange. When I got the 2nd one, it behaved exactly like the first one.

To get to the point... by digging at circuits, I eventually figured out
they needed +15 V but also +5 V on a different pin. With the two
voltages, mine now came up giving 1 PPS and also 10 MHz on a different

I have worked out that RS232 Tx and Rx signals (from a MAX3232) come out
to two pins on the external DB9 connector. I had expected it would
program like the 5650 as described here:
Thus far, I haven't seen any reply to anything I send to the unit on the
RS232 pins.

So, either these units are not programmable or I just don't know how to
talk to them. I have not found any documentation on how to program the
5680A. Does anyone have access to any more information. Did Don Latham
work out his published information about the 5650 by logic and guess
work or did he have access to something more?

I wanted to try all other sources of information before contacting FEI
as I have heard they are not that friendly unless money is involved.

If it helps, this FE 5680A rubidium was used on a Motorola SGLA4000B
High Stability Oscillator (HSO) that was (I think) used in cell sights.

thanks for any leads or comments,
-Rex, KK6MK

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