> Its relatively easy to assemble such a system. > A PC sound card can be used as a spectrum analyser for measuring phase > noise to within a few Hz of the carrier. I still need some high quality reference oscillator. Do you have any clue how much those Wenzel oscillators cost? There wasn't any prices on website, may be the only way is to ask? There seems to be interesting alternatives for the output oscillator too (to clean the LPRO signal). One of those was even named "timekeeper". Maybe it could be wise to buy one and use it for phase noise measurement first and then put it in permament use as the output oscillator of the reference, when the desired loop bandwith is known. But of course if those units has price tag with four figures or so then this is only daydreaming... :-) -- 73s! Esa OH4KJU

> -----Original Message----- > From: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] On Behalf Of Esa Heikkinen > Sent: Tuesday, January 27, 2009 2:46 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Home made GPS disciplined atomic clock > > > Its relatively easy to assemble such a system. > > A PC sound card can be used as a spectrum analyser for > measuring phase > > noise to within a few Hz of the carrier. > > I still need some high quality reference oscillator. Do you > have any clue how much those Wenzel oscillators cost? There > wasn't any prices on website, may be the only way is to ask? The run of the mill Wenzel "Streamline" series runs about $250 each. http://www.wenzel.com/pdffiles1/Oscillators/STR_4_to_30.pdf > > There seems to be interesting alternatives for the output > oscillator too (to clean the LPRO signal). One of those was > even named "timekeeper". Wenzel sells "cleanup loops" as a packaged device for a variety of frequencies. > > Maybe it could be wise to buy one and use it for phase noise > measurement first and then put it in permament use as the > output oscillator of the reference, when the desired loop > bandwith is known. > > But of course if those units has price tag with four figures > or so then this is only daydreaming... :-) I would imagine a packaged cleanup loop (oscillator and PLL) is right around $1K. I can't recall what we paid for our 10MHz widgets a few years back, but that seems about right. Clearly, one can build it yourself for less (e.g. you could use a $250 oscillator and use a PLL eval board of some sort to drive the EFC input, for instance) , but that's only if your time is free. Send Wenzel an email and ask..

Esa, > I'm wondering what could be the cause of this. According to operating > manual LPRO's output should be crystal oscillator (VCXO) generated > signal, which is synchronized to rubidium. So it is! But the detection process of the "atomic lock" is "noisy" itself. That makes it necessary to have low pass filters in this pll that make the overall noise dependend from the xtal oscillator's noise at short observation times. If you consider that a typical "normal" xtal oscillator (no oven, no temperature compensation) has an Allan deviation of 5E-8 @ 1 s then you see that 1E-11 @ 1 s IS ALREADY a BIG improvement above the "normal" case. 1E-12 @ 1 s is near the best that amateur money can buy. A lot of high grade OCXOs will be >1E-12 and <1E-11 @ 1 s and VERY FEW will be <1E-12 @ 1 s 73s Ulrich, DF6JB > -----Ursprungliche Nachricht----- > Von: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] Im Auftrag von Esa Heikkinen > Gesendet: Dienstag, 27. Januar 2009 17:34 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Home made GPS disciplined atomic clock > > > Hello again... > > > Right, it all depends on what stability you're after. The OCXO will > > have much better short-term stability than the LPRO -- the LPRO is > > close to ten times worse. So do not replace the TBolt OCXO > with a LPRO > > if short-term stability is your goal. See: > > I'm wondering what could be the cause of this. According to operating > manual LPRO's output should be crystal oscillator (VCXO) generated > signal, which is synchronized to rubidium. So why it is so much worse > than any other crystal oscillator (or other Rd oscillators). > Are there > any schematics for LPRO available anywhere? > > I cannot see the any phase noise difference between Trimble's > OCXO and > LPRO with spectrum analyser. Measured with different spans > from 500 kHz > to 200 Hz, using resolution bandwiths 300 Hz to 6 Hz. So the > noise which > is causing bad short term drift must be very close to fundamental. > > It seems that only way to see this noise is to use phase detector > circuit but my problem with that is that I haven't got any good > reference for it and this kind of equipments are quite hard > to find here > in Finland. It would be nice to see what kind of noise there are, to > design the filter bandwith for external OCXO lock circuit. > > Other idea to bring that noise visible could be multiplying > it with some > kind of comb generator circuit (might be hard to build one). Then it > would be possible to measure it's harmonics. Not sure if > there's enough > level present anymore at GHz frequencies... > > What kind of test setup did you use when getting this result: > > LPRO plots: > > http://www.leapsecond.com/museum/lpro/ > > -- > 73s! > Esa > OH4KJU > > _______________________________________________ > 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. >