[time-nuts] Trimble GPS board

Bob Camp kb8tq at n1k.org
Sat Aug 22 19:32:43 EDT 2015


The gotcah (as many here have found out the hard way) is that the OCXO is indeed a +5V part and not a +12V unit. Apparently the internal Chinese market has them mis-labeld. That bleeds over into the listings you see on eBay. There are a *lot* of mistaken listings ….


> On Aug 22, 2015, at 2:02 PM, Bob <rbenward at verizon.net> wrote:
> Hi Arthur,
> Thank you for this information.  I have not received my board yet, I probably still have a few weeks to go.  The LT1764 will take up to 20V, but I would never go to the edge.  You could easily do 12V, the only downside is the dissipation in the LT17654.  Use a variable power supply and raise the voltage slowly.  Monitor the temperature with a thermocouple,  IR spot meter (radio shack had one for $10), or just use your finger.  If you can keep your finger on it comfortable for a long period of time, the temp should be OK.  The junction temp is rated for 125C.
> Now on the flips side, my only concern is the regulator is not supplying the oven power.  Most Trimble OCXOs I see on Ebay are powered by +12.  When supplying only 6.5V the oven might not get up to temp producing frequency instability and some erratic EFC stats.
> See below, here is a 73090 OCXO (same as on some of those GPSDO boards) powered by +12V.  It's possible the regulator is meant to be powered from +12V, supplying power to the digital logic and to the oscillator portion of the OCXO. Then +12V directly supplies the oven.
> http://www.ebay.com/itm/10-000000MHz-Trimble-Double-Oven-OCXO-Trimble-73090-Double-sinewave-15V-12V-/251883335405?hash=item3aa56aaeed
> I will post my success and let everyone know how I make out.  I purchased this to have a backup for my Z3801 & Z3805.  Both are on the fritz, I will be post those trials and tribulations on a new thread.  Thanks so much for your response.
> Bob
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