On 1/22/2012 9:49 AM, Chris Albertson wrote:
The current batch of (about) $40 units are different from what was available a year ago. These new ones require 5V DC input in addition to 15V and can only be programmed via RS232 a few Hz away from 10MHz. So they are only good for use as a 10MHz reference
For historical accuracy, in Jan 2005, I bought an FE-5680A which didn't work with just a 15 V supply. After some hacking, I think I was the first (at least on this list) to figure out that it also needed 5V on one of the pins to operate. I was not able to program that one. Though reminded by these many recent emails, I haven't yet pulled it out of my stash to see if I missed something when I tried to communicate on RS-232 back then.
So the *new* ones are not that new, but they are newer than the ones, more commonly known before 2005, that worked on only 15 V and could be programmed over a wide frequency output range.
Over the years, one thing is quite obvious -- Frequency Electronics Inc. (FEI) made many similar but different versions of the FE-5680A. There seems to be no definitive way to distinguish versions that have no external physical differences (like an sma output). Also, FEI has not been responsive, to my knowledge, to any questions from us surplus consumers/hackers.
It is fortunate that this latest round of FE-5680A's seem to be consistent in characteristics and many clever people have derived a lot of details about their internals and programmatic interface. It is great that the current available surplus product seems consistent, but be aware that there were many indistinguishable iterations of the 5680A on the surplus market over the last decade or so.
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