"Best" of course is such a vague question. Best For 5MHz today is a Cesium Fountain used periodicly to calibrate 6-12 Symmetricom 5071A option 004 disciplining 5-6 Symmetricom Hydrogen Masers disciplining 5-6 Oscilloquartz 8607 option 08 BVA's. I am a part owner in just such a system. Notice the system ends with quartz and I think therein lies the key. I am a big believer that for the best system find the best piece of quartz you budget can afford. On eBay I would currently I would argue that the Datum 1000B's for around 4-500USD is the way to go. From my experience how you steer it and set up your GPS or other timing source is important but only a major factor if you do something wrong.
Thomas Knox 1-303-554-0307 > From: li...@rtty.us > Date: Sat, 29 Sep 2012 10:44:07 -0400 > To: time-nuts@febo.com > Subject: Re: [time-nuts] "Best" GPSDO > > Hi > > For close in noise, you can go from 10 to 120 to 14.5 and the net result will > be the same as 10 to 14.5. In the case of 10 to 120, close in might be DC to > 50 Hz or DC to 250 Hz. Past that a reasonable crystal oscillator could beat > the multiplied 10 MHz. In most microwave chains, the low frequency reference > only is responsible for a fairly small range of phase noise offsets. > > For most radio testing, you use wide spaced tones. What you care about is far > removed phase noise rather than close in noise. If you have a tone that's 10 > KHz to 100 KHz away from the passband, phase noise at >10 KHz is what you > would worry about. If you are building a radio with 10 Hz selectivity for 40 > Hz spaced channels, you would worry about close in noise. > > For what ever it's worth, I don't lock up the sources I use for most radio > testing. I just use free running oscillators with good noise characteristics > past 1 KHz. > > Bob > > On Sep 28, 2012, at 11:31 PM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > On Fri, Sep 28, 2012 at 5:29 PM, Bob Camp <li...@rtty.us> wrote: > >> HI > >> > >> Sort of an open ended question, but there is a fairly simple couple > >> answers: > >> > >> SInce it's close in phase noise and not far removed, things like PLL's are > >> going to transfer it directly from the reference to the output. It will of > >> course scale by 20 log N where N is the amount you multiplied or divided > >> the reference frequency by. Double the frequency and the phase noise goes > >> up by 6 db. > > > > So in my example case of scaling the 10Mhz t-bolt to 14.5Mhz Assuming > > a perfect DDS chip the T-Bolt's phase noise would be scaled up by 20 > > Log(1.45) I'm assuming this works, that I can go from 10MHz to > > 120Mhz and then to 14.5MHZ and the total effect is the same as going > > directly from 10 to 14.5, except for the noise the equipment > > introduces as added. > > > > You can guess the real question here: "how good does the 10MHz > > reference need to be to test real-world receivers? > > > > > > > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > 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.
