Adding 1 PPS and 10MHz Outputs to the Z3801A

Posted on Feb 7, 2014

Make Z3801A GPS-disciplined oscillators more useful by making 1 PPS and additional 10MHz signals available on the rear panel, and providing a 1 PPS signal on the DCD line of the serial connector so the unit could serve as a reference clock for an NTP server. Although I ultimately want to add a distribution amplifier/splitter for the 10MHz sine wave signal, I thought it would be easier to initially add several

Adding 1 PPS and 10MHz Outputs to the Z3801A
Click here to download the full size of the above Circuit.

10MHz TTL square wave outputs. This page describes how I did that. Jeff Mock has published a modification that provides a nice RS-232 level 1 PPS signal on the DCD line, so I used that as the starting point. (Note: I`ve learned that Jeff`s web page is no longer there. A mirror is at. ) Jeff taps a 1 PPS TTL level signal off of U5, pin 2 (a Lucent 1141LL, whatever that is). I used that signal to drive my 1 PPS circuit. After probing around on the board, I was unable to discover a 10MHz TTL level square wave anywhere. However, TP5 in the front portion of the main board has a nice 10MHZ sine wave available, which unfortunately is riding on top of a DC bias voltage. I used a piece of RG-174 cable to bring the signal from TP5 back to my circuit. The front pin of the adjacent TP4 complex is at ground, so I connected the RG-174 shield there. The 1 PPS circuit is very simple. I used a 74AC04 hex inverter, with the first section providing an initial inversion so that the end result remains a positive-going pulse. The output is a pair of inverters parallelled together through 51 ohm resistors; this combination provides a nice low-impedance signal that can drive a reasonable length of coax. The unused sections of the 74AC04 must be tied to something; if they float, the chip may oscillate or otherwise find itself in a state of high current draw. I tied the unused inputs to the output of the first inverter, so they are available as...

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Stereo Led Vu Meter
    DS1621 IIC interface under Linux drives designing
    170w audio power amplifier
    LM56 diagram of Circuit of the Thermostat project
    Audio clipping indicator circuit
    Water Level Detector With Alarm
    AM balanced diode circuit