[time-nuts] Z3801A OCXO manual trimming

Tom Curlee tcurlee at sbcglobal.net
Mon Mar 5 23:18:36 EST 2018

What is the rail to rail EFC voltage on the Z3801A?  Is it different than the single oven 10811?  My 10811 manual says that the EFC is -5V to +5V, while the EFC voltage on my ailing Z3801 is ~-2.0V with LH reporting the DAC at 99.996902%.
Haven't had time to dig any further - been moving/installing antennas including one of my GPS antennas.

      From: Mark Sims <holrum at hotmail.com>
 To: "time-nuts at febo.com" <time-nuts at febo.com> 
 Sent: Monday, March 5, 2018 7:36 PM
 Subject: [time-nuts] Z3801A OCXO manual trimming
Or, it you are sure it's the OCXO,  go shopping for a new one.    There is a reputable seller with them (the double oven version) for $100 on Ebay.

A couple of things to try...  monitor the EFC voltage, power up the unit, and see if it is changing as it attempts to lock.  If  it does not, you may have a DAC problem... I don't think the Z3801 remembers the last DAC voltage to speed up the initial lock, so it should be searching for the lock voltage.

Also monitor the OCXO output and see how it changes as it warms up.  It should start out several Hz off and converge to 10 MHz as it warms up.  


> Either tear into the OCXO or go shopping for a new(er) GPSDO.
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