Hello, Why would you not want high drive level for best close-in noise? This is at odds with general thinking in the industry. Close-in in this context means from 0.1Hz to 1/f knee which is 1-100kHz depending on the design of the sustaining amplifier.
There are few reasons why low phase noise "practical" oscillators are built as OCXOs: On one hand: - close-in noise depends on 1/f knee frequency - lowering knee frequency requires high-Q resonators - for classic 1MHz..100MHz range this means crystals - high-Q crystals require SC-cut On the other hand: - phase noise density is measured as a ratio referred to carrier level - increasing carrier level improves phase noise figure - increasing carrier level necessitates increasing drive level - maintaining reasonable ageing rate at higher drive levels requires SC-cut crystals Having established that SC-cut is preferred: - SC-cut has high temperature turning point. Its room temperature tempco is much worse than AT-cut's one making it mostly unusable as XO or TCXO - High temperature turning point requires oven Leo >> From: Bob kb8tq <[email protected]> > It depends a lot on the offset you are looking at. For close in phase noise, > you probably don’t > want high drive. If you are only after phase noise past 10KHz, you may not > want / need > an OCXO in the first place. Selecting crystals (like one in a hundred) for > very high drive / > low phase noise setups *is* done. It’s just not very practical. > > > On Jul 10, 2019, at 3:49 AM, Leo Bodnar <leo at leobodnar.com> wrote: > > It depends whether OCXO is designed for long term stability and low ageing > > or low phase noise. > > Low ageing requires low drive but low phase noise needs as much drive as > > humanely possible - often approaching mW levels. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
