[time-nuts] oscillators

Bob Camp lists at rtty.us
Fri Aug 31 10:06:46 EDT 2012


Hi

An SC is going to have it's temperature curve centered up around 95C or so. If it's been cut as an OCXO crystal the turns will be up there as well. By the time it gets to room temp, the delta F / delta T is moving mighty fast. Think in terms of multiple ppm/C. A typical cell phone TCXO crystal is in the sub 0.1 ppm/C range in the vicinity of room temp.
In addition, SC's are pretty hard to pull. For a normal TCXO (no DDS) something > 40 ppm of range would be needed. By the time you get the wide tune stuff in the circuit, the phase noise isn't going to be anything special. 

Bob

On Aug 31, 2012, at 12:10 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 8/30/12 9:04 PM, Bob Camp wrote:
>> Hi
>> 
>> A standard clock crystal is pretty much junk. as far as temperature performance is concerned. Even a cheap TCXO is likely to be pretty good over 25 C +/- 10C.
>> 
> 
> yes.. but, say, one had a decent SC cut with good phase noise properties, but large (but repeatable) temperature characteristics.
> 
> Can I get good accuracy AND good phase noise, for less hassle/power/size than an OCXO?
> 
> My radio has a TCXO and a clock oscillator, so the clock oscillator is my test article for the temperature compensation scheme..
> 
> 
> 
>> Bob
>> 
>> On Aug 30, 2012, at 11:35 PM, Jim Lux <jimlux at earthlink.net> wrote:
>> 
>>> On 8/30/12 6:12 PM, Bob Camp wrote:
>>>> Hi
>>>> 
>>>> If the temperature is varying slowly *and* there are no gradients you may get your order of magnitude over some range. You might be surprised at your TCXO. A lot of them are pretty darn good in the vicinity of room temp. You may already be an order of magnitude past your ppm or two for fairly normal temperature changes.
>>>> 
>>> 
>>> Temp does vary slowly (the radio weighs on the order of 6kg)..
>>> 
>>> Need to hold spec (in theory) from -20 to +40C.  The oscillator runs about 10 degrees hotter inside.
>>> 
>>> About 0.2 ppm from 5C to 40C.  +/- 1ppm worst case over the whole temperature range.
>>> 
>>> What I'm also interested in is whether I can compensate a non TCXO 66MHz CPU clock oscillator (even cheaper, potentially better phase noise with a higher Q crystal, etc.)
>>> 
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>> 
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> 
> 
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