HP Clock

Thursday, February 10, 2011

Lab Clock Near Completion

A precision time source for the lab is up and running.  I'm using a surplus GPSDO (Global Positioning Satellite Disciplined Oscillator).  These units came out of cell sites and were used to keep the cell sites in step with each other.  The GPSDO is monitored by a surplus DL360 server picked up at a swap-meet for $40.

The server uploads the status to my web site so that I can monitor the GPSDO from a web address. The uploaded data shows the position of the satellites as well as the crystal aging.

The next step will be to put a distribution amplifier with built in divider chain.  This will take the 10 MHz from the GPSDO and feed it to multiple instruments.  I've built the distribution amplifier by modifying an old video distribution amp.  I replaced the 75 ohm build out resistors with 50 ohm resistors.  I also added a 50 ohm one to one transformer on each output so that I can eliminate ground loops when feeding multiple devices.  The divider chain gives me precision frequency outputs at 1 MHz, 100 KHz,
10 KHz, and 1 KHz.

The final piece of this project will be to derive 60 Hz from the 10 MHz master output. (Useful for monitoring the power grid, and driving conventional clock circuits.)  I plan to do this by extracting the third harmonic from the 100 KHz square wave, and then dividing the resultant 300 Khz signal down to 60 Hz.