Alberto Although you might not be a specialist, you do make it understandable. My question regarding this unit was not as stand alone, but being 'managed' or corrected by either the 10 khz signal from Jupiter or 1 pps, or perhaps some more elegant way. Just the heart, not the beat! (smile)
Thanks Eric -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Alberto I2PHD Sent: Saturday, November 26, 2005 4:23 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] ebay 10MHz-OCXO- ecellison wrote: > Alberto et.al. > > What do you think about this part? It is about $17 new. > > http://www.cmac.com/mt/news/cfpt-125.html > > Thanks > Eric2 > Eric, as always, it all depends on what you want to do and how you plan to do it. For a lab grade frequency standard, what you want is that the frequency variation is ideally zero, which is not possible of course to achieve in practice, so you want it as low as possible. If you look at how a GPSDO works, you can make a parallel with a heavy flywheel (the quartz oscillator), whose angular speed (which you want to keep as constant as possible) is checked and corrected every few seconds (30 in the Shera design, more frequently in other designs). You can easily see that between corrections the flywheel must keep its angular velocity unaided, and this imposes stringent requirements on its construction and characteristics. So, a GPSDO cannot be built using a cheap oscillator, you must start with a very high quality one, otherwise the risk is that the loop doesn't lock. The correction done every few seconds is just a very small and gentle nudge to the oscillator. If the frequency offset of the oscillator is too great to be corrected by this nudge, the lock is lost. I am not a specialist of this field, so take my assertions with a big grain of salt, but, IMHO, the stability of 9 parts on 10^7 specified for the oscillator you mention is a bit on the low side. You need something better, at least with a design similar to Shera's. If you are willing to accept a greater phase noise and a worse short term stability, then you could use some other designs for the GPSDO, like that that uses the 10 kHz from the Jupiter GPS unit. Probably the C-MAX MicroTechnology TCVCXO can work well in that circuit. Of course all of this is pure academy if all what you want is not to build a lab grade frequency standard, but just a stable oscillator for your HF radio. Commercial TCXOs with a stability of 0.1 ppm are more than enough for this purpose. Things start to be a bit different if what you want to do is coherent demodulation of a signal at 24 GHz.... 73 Alberto I2PHD _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
