Hi Here is a little more on how much of a problem you have.
If you would like the spurs to be down 70 dbc at 10 GHz. They go up by 20 log N. in this case N is 1000. That gets you 60 db. Spurs at 10 MHz would have to be down at -130 dbc to make it at 10 GHz. If you want noise over 10 KHz to be 60 db down, it goes by 10 log BW. That gets you to 1 Hz noise at -100. The same 60 db to 10 MHz then applies. You would need -160 dbc phase noise at 10 MHz to hit that. Both of those would be hard to hit with any Rb. Fortunately you can use a multi step multiplication chain. Once you make that decision, noise and spurs on the Rb are not a big issue. Bob On Feb 7, 2012, at 1:52 PM, John Ackermann N8UR <j...@febo.com> wrote: > I am just finishing my promised stability and phase noise measurements on a > batch of inexpensive Rb standards; I hope to publish the results tomorrow > evening. > > In the meantime, I've looked at two of the FE-5680s and their phase noise is > significantly worse than either the Efratom FRS or the Datum LPRO -- in > particular, there is a forest of spurs all the way from 1 Hz on out, most of > them at around -80dBc or worse. By the time you multiply that to 10 GHz, > that's only about 20 dB below the carrier! Apart from the spurs, the noise > floor is significantly higher than the other two types. > > A clean-up oscillator would be an interesting add-on. > > John > ---- > > > On 2/7/2012 12:48 PM, C. Turner wrote: >> Hello, >> >> As has been mentioned here before, the output of the "non-tunable" >> FE-5680A's has been noted to have low-level spurs in it - no doubt due >> to the way the various frequency loops are derived within, some using >> DDS techniques. It is for this reason that when I packaged my FE-5680A >> in its own, stand-alone enclosure I included a fairly narrow band (+/-6 >> kHz @ -6dBc) crystal-based bandpass filter in the output. >> >> After more recent testing of two FE-5680A's using two different 10 GHz >> microwave transverters, I've determined that this filtering just isn't >> enough. At first, it was assumed/hoped that the racket that I was >> hearing was coming from somewhere else - perhaps the switching >> up-converter or some other interaction - or just something "odd" about >> my homebrew 10 GHz transverter, but this is, unfortunately, not the case. >> >> In testing with a DownEast Microwave 10 GHz transverter fitted with an >> N5AC synthesizer, the CW notes sounded nice and clean when locked to the >> Z3801 and there was only a trace of modulation that I'd not really >> noticed before when I used the Efratom LPRO-101, but when the '5680A was >> connected, the incidental PM was bad enough that it was difficult to >> determine where, exactly, zero beat was! Since the synthesizer uses a >> fairly high reference frequency internally there was little impediment >> to the low-level phase modulation on the reference. >> >> I compared this with my own homebrew 10 GHz transverter. This unit uses >> an 18.4 MHz Butler VCXO that is multiplied to 110.4 MHz which is then >> fed to a "brick" oscillator with the 110.4 MHz being compared to the 10 >> MHz reference using a harmonic mixer, locking to the 400 kHz residual. >> Since this unit has a comparatively low loop bandwidth in the VCXO the >> grunge was considerably reduced, but still objectionable, giving some >> hope that a simple VCXO scheme might make the '5680A usable. >> >> I still have yet to do a more-detailed analysis of the phase modulation >> that is appearing on the 10 GHz signals, but I can clearly hear a low >> frequency modulation source (perhaps the lock-in amplifier) plus a >> myriad of other audio frequency components and their harmonics. Again, >> with the LPRO-101 was very "clean" by comparison and I could *just* hear >> some similar, very low-level noises in the background that I'd not >> really noticed before. >> >> As it is, the '5680A-based reference is unusable with the N5AC >> synthesizer and its wide loop bandwidth and "almost" usable with my >> homebrew transverter and its comparatively narrow loop bandwidth. I'm >> now bent on making the '5680A usable as a microwave reference, but my >> current plans are to build a simple 10 MHz Butler VCXO and then lock it >> to the '5680A using a very "slow" loop filter: In that way, I'm hoping >> that the phase noise will be largely that of the 10 MHz VCXO and its >> cheap CPU-type crystal rather than the '5680A! >> >> Clint >> KA7OEI >> >> >> _______________________________________________ >> 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.
