Bruce, thanks, I'm soaking it all up. 73, Steve
2009/1/10 Bruce Griffiths <[email protected]>: > Steve > > Steve Rooke wrote: >> Bruce, >> >> Thanks for the detailed rundown. Looking at the picket-fence method, >> this looks possible for me but I will have to get hold of the >> reference standard. I have a Racal-Dana 1992 with IEEE488 but need to >> get an interface card for the PC end. These are fairly cheap to buy. >> >> You spoke about some types of rubidium standards being suitable, would >> you care to elaborate on that please? Would something like an Efratom >> FRS be suitable? Generating the picket-fence itself should not be >> hard as long as care is taken not to introduce noise. Do you have any >> links to articles on the design for the >> mixer/zero-crossing/square-wave beat circuit? One question, assuming >> that I have a 10MHz reference standard and I'm measuring a 10MHz dut, >> how do I arrange for them to be about 1Hz apart, given that we are >> measuring for accuracy here? 1HZ different would make the accuracy >> 1E-7 out anyway, or am I missing something here? >> >> > The best article I've come across on zero-crossing detector design is: > > The Design of Low Jitter Hard Limiters" Oliver Collins, IEEE > transactions on Communications, Vol 44 No 5, May 1996 pp 601-608 > > Unfortunately its not free, however you may be able to access it via a > Library. > > However if you only want to use the technique described in the paper, I > have a couple of spreadsheets that calculate the stage gains and low > pass filter time constants both for the simplified analysis in the paper > and the more general case where the input noise spectral density differs > for each stage. > Some pointers on what to include in the noise calculations for each > stage can be found at: > > http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html > <http://www.ko4bb.com/%7Ebruce/ZeroCrossingDetectors.html> > > Some care is required, in that if the spreadsheet predicts a gain of > less than unity for the input stage, it is in fact better to use a > passive RC low pass filter in front of the first amplifier limiter stage > (without a clamp as typically the IF signal amplitude at the mixer > output is insufficient to cause the clamp diodes to conduct - more > complex clamps are too noisy). > The amplifier limiter chain is then redesigned to accommodate this change. > > Don't be taken in by those who would insist that everything should be > linear as long as possible, the resultant deign is suboptimal. > Such comments sprang from the fact that no one at that time had worked > out how to include the effect of the clamps on the performance. > Oliver Collins solved that problem, so there is no longer a valid excuse > for such misguided recommendations. > >> So the real thing for the budget-conscious time-nut seems to be the >> reference standard. The ocxos you spoke about do seem to be on the >> rare/expensive side and are an order of magnitude or two better than >> the Option 4E I have in the 1992. >> >> 73, Steve >> > Bruce > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW Omnium finis imminet _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
