[time-nuts] Short-Term Stability

Mike Feher mfeher at eozinc.com
Thu Mar 16 10:24:07 EST 2006

Hans -

I built my first DDS back in 1970 (at acoustic frequencies) and have been
around them ever since. The rule of thumb that I remember and verified often
is 6/dB per bit and not the 9 dB that you mention. Even the 6/dB theoretical
number is tough to meet with higher clock frequencies. I also do not
remember a limit on the noise floor in dBc as with 12 bit D/As we did
achieve spurious that was typically around 70 dBc. There are several
mechanisms that cause the spurious, including the phase and amplitude
truncation due to the finite amount of bits, in the accumulator as well as
the D/A, as well as what is know as the crossover spurious. Crossover
spurious are very predictable as to location. Aliasing also causes spurious
to appear in-band. Regards - Mike    

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Hans H. Jucker
Sent: Thursday, March 16, 2006 9:49 AM
To: time-nuts at febo.com
Subject: [time-nuts] Short-Term Stability

Attached some thoughts about short-term stability of microwave frequency

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