AADE Precision Frequency Reference.
Assembled and calibrated against my Rubidium frequency standard
to better than 0.1 parts per million (1Hz at 10MHz)
with long term accuracy of 1 part per million (1Hz at 1MHz)
Switch selectable output frequencies of
Output is .5V p-p square wave into 50ohms
NOTE: the frequency reference does NOT include a wall transformer or power supply. You get a chance to use one of your collection of old wall transformers from cordless phones etc.
Input power can be anything from 6 to 18 VDC or 6 to 12 VAC. Simply cut off the connector from the wall transformer, observe polarity of DC supplies, and solder to the power inputs on the reference PCB.
I do not have long term experience with this unit but it uses the same precision oscillator used in my line of frequency counters.
Above is a DFD4A I built 4 years ago and calibrated against my rubidium frequency standard to read
It now reads 10,000,003 Hz. 3 Hz drift at 10MHz after 4 years (0.3 parts per million).