[time-nuts] HP E1938

Larry McDavid lmcdavid at lmceng.com
Sat Apr 15 21:01:59 EDT 2017

The units now available on eBay have various types of D-Subminiature 
connectors and can be on either side of the board. I will have to wait 
until my unit arrives to see what I get. It should be possible, if 
necessary, to remove the connector and replace it with a more convenient 
D-Submin connector on the desired side of the board.

I did not originally note the additional zip'd info available from that 
eBay website but now have those files. Thanks for that link.

So far, I have not seen any spec for the EFC voltage and polarities used 
in the "Integrated PWB." Anyone know that?

The "full instrument" version also available now on eBay is a complete 
GPSDO but at $130 plus $80 shipping. I really don't need yet another 
GPSDO but would use the integrated PWB assembly for a low ADEV 
free-running 10 MHz source. I have a HP 10811D for that now but will 
evaluate this new unit for performance.

Anyone have experience doing this and know the EFC requirements?


On 4/15/2017 4:01 PM, Richard (Rick) Karlquist wrote:
> It's been 20 years, but I will try to recap what I remember
> about this connector.  I believe there were 3 customers,
> and one of them required the DB connector with coax inserts
> for reasons of backward compatibility.  I think this
> vendor was Motorola.  We did not actually use the coax
> inserts, but left them blank and ran the RF, etc on
> ordinary pins.  I believe you can make an ordinary male
> DB-25 mate with these insert versions by clipping off some
> of the pins that would be blocked by the female insert
> version.  I vaguely remember that the other 2 vendors
> used gender changers or something.  There might have
> an issue with the mating plane location being different
> for different customers.
> I am sure that time-nuts, being talented at repurposing,
> will be able to think about this problem and come up with
> a simple solution to interfacing with these boards.
> No need to buy insert type connectors.  I never had
> any trouble making cables that connected to these units
> using plain vanilla DB25's.
> Rick N6RK
> On 4/15/2017 10:42 AM, Larry McDavid wrote:
>> Ok, so a standard DB 25-pin socket-contact connector will mate with the
>> on-board connector with the center hole and missing pins. That's good!
>> I now notice a comment on your webpages about this device in which you
>> mention a schematic. Do you have a schematic of this board? If so, can
>> you point to it or send me a copy.
>> I was unaware of the complete packaged unit on eBay; thanks for that.
>> Another poster mentioned the wiring of the connector on the full
>> instrument version power connector; is that pin-out and spec available?
>> Larry
>> On 4/15/2017 5:05 AM, Tom Van Baak wrote:
>>>> I purchased one of these HP E1938 OCXO recently on eBay but have not
>>>> yet
>>>> received it.
>>>> Is that special D-Submin connector a receptacle-shell, pin contact
>>>> version? Will a standard plug-shell, socket contact 25-pin D-Submin
>>>> fit it?
>>> Hi,
>>> I'll cc the group here since we may get some useful comments.
>>> I'm not exactly sure what you mean. The E1938A oscillators that I've
>>> seen and tested look like this:
>>> http://www.leapsecond.com/museum/e1938a/
>>> And those can be interfaced with a simple D-sub DB25 connector on the
>>> PCB. For connections, see that page, or any number of postings about
>>> the E1938 in the time-nuts archives.
>>> Note that on eBay there are at least three variations of E1938A
>>> oscillator. The item#'s below are just random search picks (I have no
>>> affiliation with any buyers or sellers) and I also know not all
>>> surplus refurbished surplus recycled surplus stuff works. But we do
>>> this because when they did work, they are sometimes totally amazing.
>>> 1) There's the bare "puck" alone, as in
>>> http://www.ebay.com/itm/290829077542 -- and I have no idea where one
>>> would start with that item since all the support circuitry on the PCB
>>> would have to be re-created by hand.
>>> 2) There's the integrated PCB assembly, as in
>>> http://www.ebay.com/itm/181043193416 -- which is more like what I
>>> tested.
>>> 3) There's the full instrument version, as in
>>> http://www.ebay.com/itm/171293069062 -- which is most likely to work,
>>> or be less hacked up, or dented, or salvaged, or rusted. It even has
>>> all the connectors and power supplies, and GPS, etc.
>>> If any other time nuts have experience with each of these methods to
>>> obtain a E1938 oscillator, please let us know.
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Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)

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