Hi > On Jan 20, 2017, at 11:22 AM, Tom Miller <tmiller11...@verizon.net> wrote: > > > ----- Original Message ----- From: "jimlux" <jim...@earthlink.net> > To: <time-nuts@febo.com> > Sent: Friday, January 20, 2017 8:34 AM > Subject: Re: [time-nuts] Thunderbolt Harmonics > > >> On 1/19/17 8:48 PM, Rhys D wrote: >>> Thanks for the detailed post Bill, >>> >>> I'm learning a lot here! >>> So the spectrum analyser is indeed a "trap for young players" >>> As you guessed, it is a Siglent SSA3000X series analyzer. >>> >>> I just looked at the same signal again with varied attenuations dialed in >>> on the instrument (I am using an external 20dB attenuator from minicircuits >>> as well) >>> >>> Here is what I saw: >>> >>> Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic >>> 15 dB - 11.40 dB - 49.13 dB - 51.12 dB >>> 20 dB - 11.40 dB - 48.84 dB - 56.48 dB >>> 25 dB - 11.28 dB - 48.32 dB - 49.15 dB >>> >>> I guess these numbers mean I can't really trust what I can see on the >>> instrument screen? >> >> Actually, that's fairly good. Most spectrum analyzers are good to about 1/2 >> dB with a moderate level signal (your fundamental). >> >> The variation you're seeing is probably some combination of: >> 1) the mismatch between the source impedance and the spectrum analyzer input >> impedance - the latter of which almost certainly changes with attenuation >> setting >> 2) The calibration of the step attenuator. >> 3) maybe some change in harmonic production in the SA front end... in your >> case, though the harmonic levels go DOWN as the attenuation is decreased, >> which is the opposite of what happens with harmonics >> > > If you want to see the levels of the harmonics you should notch out the > fundamental.
….. and use a notch filter that does not miss-terminate the output amplifier (as most notch filters do …) Bob > > Regards, > Tom > > _______________________________________________ > 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. _______________________________________________ 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.
