[time-nuts] Good clean-up oscillators

[Bob kb8tq]

Hi

There are indeed TCXO’s out there that have exactly the same crystals in them
as OCXO’s (other than the cut angle). They are not super common. AT based
OCXO’s are not as popular as they once were. Large(r) package / high price  
TCXO’s also are not what most people go out and buy. 

All that said, there are at least several million TCXO’s with 10 MHz 3rd overtone 
AT cut OCXO crystals  “out in the wild”. They were produced over at least a 30 year 
period.They went into a variety of applications. They may still be in production somewhere. 

With a TCXO, you have a wide range tuning circuit fed by a temperature compensation
network of some sort. That and the lack of thermal buffering are what degrade 
the close in performance when you *do* use a fancy crystal. 

Bob

> On Feb 18, 2019, at 10:24 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Wed, 23 Jan 2019 17:31:04 -0500
> Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> If you take a look at typical TCXO’s and XO’s in a real world environment, 
>> their noise is higher than a similar 
>> OCXO even at 100 Hz. If you are cleaning up something like a Rb, your loop 
>> may well be below 1Hz. 
> 
> I always assumed, this is because they use cheaper resonators, with 
> lower Q for the XO and TCXO than for the OCXO. E.g. most HC-49 case
> AT-cut crystals are in an (inert) gas at approximately 1bar pressure.
> My guess would be, if the same crystals would be used, the phase noise
> levels should be comparable down to 100Hz at least, maybe even 10Hz.
> 
> If my guess is wrong, what would be the reason?
> 
> 			Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
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> 
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