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Old 29th Jan 2023, 8:20 am   #13
Radio Wrangler
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Default Re: Crystals for David Looser Modulator

Quote:
Originally Posted by Niechcial,Steve View Post
Thanks Tony and G6. The programmable oscillators look fun to play with. I will probably opt though for the crystals> Help much appreciated.
Be careful. The 'programmable crystal oscillators contain a phase locked loop with programmable dividers and a VCO.

On-silicon resonators for VCOs are rather limited in the Q they can achieve and this means that the overall phase noise performance they can achieve is much poorer than a straight-forward crystal oscillator alone.

All the counters ackling away on the same die aren't perfectly isolated, so a variety of spurs can be found on the output.

On the plus side, for each different frequency a manufacturer makes for the actual crystal oscillator inside the programmable oscillator package, they can sell them as a large number of frequencies within reach of the VCO's range and the choice of N/M ratios.

Be especially careful because numerous oscillator families in supplier data sheets are now programmable ones. The data sheets often fail to mention thatyou are not getting a simple crystal oscillator.

For noise-critical RF applications, it can be a bit of a devil looking through all the oscillators in stock at a distributor, wondering which ones are quiet.

David
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