Harmonic traps are another avenue to explore since the frequency is "fixed" at well below ppm. Which leaves the fundamental untouched.
On Wed, Jan 18, 2017 at 5:21 AM, Charles Steinmetz <csteinm...@yandex.com> wrote: > Rhys wrote: > > I was looking at the output of my Trimble Thunderbolt GPSDO and was rather >> surprised to see really "loud" harmonics in there. ~ 60dB down from the >> 10Mhz signal. >> > > Welcome to the world of RF. Loudest harmonic at ~ -60dBc (dB with respect > to carrier) is actually pretty good for a commercial product. Very few > distribution amplifiers do this well. For that matter, many good > laboratory RF generators are specified with harmonics only below -35 to -45 > dBc. We do not generally expect RF sources or amplifiers to get down to > the -80 to -90 dBc range (although amplifiers with harmonics < -80dBc at > 10MHz/1Vrms/50 ohms are possible), and certainly not the -100 to -120dBc > that we expect from high fidelity audio sources and amplifiers. > > Even harmonics (which make the carrier asymmetrical) can cause phase > errors that are harmful in high-precision systems [1], so I am a vocal > supporter of distribution amplifiers with harmonics < -80dBc. > > Note that cleaning up the Tbolt output to < -80dBc would probably require > a crystal filter (a filter with a sharp corner very close to 10MHz, in any > case), which means its phase response changes very rapidly with the filter > frequency. Sharp filters shift frequency with temperature, which causes > temperature-dependent phase shifts. Unless the filter is maintained in an > isothermal environment (like a good oven), this can cause problems in > sensitive applications. > > Best regards, > > Charles > > > [1] F.L. Walls (NIST), F.G. Ascarrunz (SpectraDynamics), The Effect of > Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis > (year unknown, probably late '90s). > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.