Today's experiment is a 10 MHz low pass filter to clean up a square wave and turn it into a sine wave.  This comes from the realization that the reference output from my Racal Dana 1992 universal counter is very unclean square wave instead of a pure sine wave.  Because square waves are actually composed of numerous harmonically-related sine waves, a good filter can extract just the fundamental tone of interest.  Cool, huh?

Why is this important?  Let's delve in a bit further . . .

This is a refinement to an earlier 40 dB coupler that I built in 2013.  That first one was taken directly from the May/June 2013 issue of QEX Magazine.  Inside, there was an article from Loftur Jonasson (TF3LJ / VE2LJX) about building a simple digital RF power meter.  Jonasson's article referenced and built on earlier work by W7ZOI and W7PUA (published in the June 2001 issue of QST).

This is a little experiment at building a circuit that seems easy, but may not actually be that simple.  I needed 0° power splitter for my 10 MHz precision frequency standard project.  I picked up a Minicircuits ZFSC-2-1 on eBay which solved my immediate need, but the allure of experimentation is too strong to resist!

Yesterday (8/28/14), I did a lot of testing on the repeater's power supply.  It works!  And in my usual style, I have lots of data:


This started as a quest to build an atomic frequency standard based on a rubidium oscillator.  After realizing that I could get much better short-term stability and long-term accuracy by building around an ovenized crystal oscillator that's disciplined to a GPS time reference, the project was retargeted.