Hi I think that the issue is not so much harmonics, as spurious signals on the output (signals not equal to N times 10 MHz). Harmonics by themselves are not a big deal.
Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of shali...@gmail.com Sent: Tuesday, November 15, 2011 11:12 PM To: Time-Nuts Subject: Re: [time-nuts] FE 5680A "new version" - Filtering the 10 MHz I am trying to understand the problem with harmonics on the 10 MHz output. If you use it to drive the external input of another instrument, it won't be a problem, more likely it will probably help since the instrument will convert that signal to a square wave more appropriate to driving digital logic anyway. If you use it to drive a mixer, mixers are highly non-linear devices that will generate their own harmonics, and most mixers actually show improved performance (like reduced conversion loss) when driven with a square wave. So what is the problem? Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -----Original Message----- From: "Charles P. Steinmetz" <charles_steinm...@lavabit.com> Sender: time-nuts-boun...@febo.com Date: Tue, 15 Nov 2011 16:15:37 To: Discussion of precise time and frequency measurement<time-nuts@febo.com> Reply-To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Subject: Re: [time-nuts] FE 5680A "new version" - Filtering the 10 MHz Robert wrote: >One "off the shelf" or more likely out of the junk box option is to >use the filter components from a 10Mb/s ethernet card. They work >quite well but might introduce some temperature related phase shifts. As others have pointed out here in the past, to minimize phase and amplitude shifts with temperature changes, you would like the phase and amplitude responses to be changing as gradually as possible in the vicinity of the oscillator frequency. However, this is not the case with a bandbass filter centered on the oscillator frequency or a low-pass filter with a cutoff near the oscillator frequency. If the undesired output components are harmonics, you can reduce the first few with traps (i.e., notch filters). This may be all you need (for example, if the harmonics were generated by a buffer amp with simple nonlinearities). Even if there is an extended harmonic series, as may be the case with the 5680A, it will allow you to filter the higher harmonics using a low-pass filter with relaxed specifications (higher cutoff frequency, fewer poles, and/or better damping), thus preserving gentle phase and amplitude response at the oscillator frequency. Best regards, Charles _______________________________________________ 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. _______________________________________________ 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.