There isnt any; that's not a correct assertion for crystal oscillators in the general case.
The math associated with multiplying or dividing a frequency is pretty straightforward. If an input edge is N picoseconds late due to jitter, the corresponding output edge is also going to be N picoseconds late within the bandwidth of the device. So it's easy to see how phase noise in dBc/Hz is related to the percentage of one cycle that a given edge is early or late. Double the duration of a cycle, and the effect of a constant jitter deviation is halved, or reduced by 6 dB by the usual 20*log(N) amplitude rule. Halve the duration of a cycle, and the effect of the jitter is doubled. Crystal oscillators do not behave anything like dividers or multipliers, unless they have dividers or multipliers built in. Only the >160 MHz Wenzel oscillators use built-in mulipliers, I believe, and none of them use dividers unless you order one explicitly as a separate part. Higher-frequency crystal oscillators are generally cleaner at offsets beyond a few kHz. Only at close-in offsets do the 5 MHz ULNs have an advantage over the 10 MHz ones, and there are no hard-and-fast 6-dB relationships as a rule. -- john, KE5FX (got a lot more stuff to post, but it's going to take awhile to get it together...) > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Behalf Of Tom Van Baak > Sent: Tuesday, January 01, 2008 11:22 AM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] xtal oscillator phase noise > > > > Tom - > > > > Nice data. It really confirms what I initially posted. Your measurements > > were at 5 MHz, so, the expected number at 10 MHz would be 6 dB > worse. The > > -155 dBc/Hz number quoted by memory from me then was not that > far of at all. > > - Mike > > Hi Mike, > > What's the math behind why an equivalently good 10 MHz > reference is always(?) 6 dB above a 5 MHz reference? > > /tvb > _______________________________________________ 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.