To Bob kb8tq Figure Of Merit sounds like a useless number. I have a different approach that yields immediate and useful results. Before I explain my method, let me introduce myself.
In 1970, I invented, and Memorex patented, the original zero-deadband phase-frequency detector. You can see it in page 3 of my '234 patent at https://patents.google.com/patent/US3810234A/ This invention soon led to another invention of tremendous significance to today's world. In 2014, researchers published a study in the journal Supercomputing Frontiers and Innovations estimating the storage capacity of the Internet at 1e24 bytes, or 1 million exabytes. When I started working for Memorex, an IBM 2314 disk pack could store 29.2 million bytes. At that rate, today's internet would require 1e24/29e6=3.44e16, or 34,400,000,000,000,000 IBM 2314 disk drives. This is an impossible number. Other estimates give equally outrageous numbers. The problem in those days was improvements in disk drive capacity were basically trial and error. This is a slow and very expensive business. My new invention allowed peering into the hard disk and separating out all the variables that affect performance. With this information, researchers could see the effect of changes and quickly optimize the performance. This allowed the tremendous improvement in tape and disk drive capacity that now allows the internet to store all the needed data. You can see how this invention works in the Katz paper at https://tinyurl.com/2bmuz3n2 Now for my new method. The schematic for a phase-frequency detector is shown in DBAND2S.PNG. In operation, a pulse arrives at the DATA pin and pin U1Q goes high. Then a pulse arrives at the VCO pin and pin U2Q goes high. This allows the NAND gate to bring the CLR signal low, which immediately resets both d-flops. The result is shown in ZERODB.PNG. It is a very narrow pulse with both d-flops superimposed. This is the basis for my new approach. Simply tie both inputs of the PFD together and measure the noise spectrum of the output. (Of course, you have to ensure that both outputs match at zero error.) Once you have the PFD noise, you can enable the loop and measure the total noise spectrum. Then simply subtract the PFD spectrum to get the OCXO noise. If you have two identical VCXO's, each one contributes half the noise. I don't know if this method would work with a double-balanced mixer. The problem is a DBM requires quadrature signals, so the noise is a function of the OCXO noise as well as the mixer diodes. But the OCXO noise is what you are trying to measure. This method works with the PFD since only a single pulse is needed to activate both d-flops, so you are measuring only the PFD noise. Et Voila. Now that you can measure the OCXO noise, you might want to try your hand at designing an oscillator with minimum noise. You immediately run into a problem. The high Q of the crystal means the oscillator takes a very long time to start up. I solved this problem in my OSC.ZIP file at https://tinyurl.com/2p9yrxmy Steve Wilson is me. Just start at the README.TXT file and you are on your way. Now that you are a fully qualified Time-Nut, you might be interested in some of the following papers: Rohde, 1994 How to improve phase noise by multiple varicaps in parallel http://www.arrl.org/files/file/Technology/ard/rohde94.pdf Leeson Equation http://rfic.eecs.berkeley.edu/~niknejad/ee242/pdf/eecs242_lect22_phasenoise.pdf Oscillator Phase Noise: A Tutorial Thomas H. Lee, Member, IEEE, and Ali Hajimiri, Member, IEEE http://smirc.stanford.edu/papers/JSSC00MAR-tom.pdf Hajamiri Virtual Damping and Einstein Relation in Oscillators https://authors.library.caltech.edu/523/1/HAMieeejssc03.pdf
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