[R-390] 200KC calibration crystal source

[Bob Camp]

Hi

The 17 MHz crystal is an AT cut, so it has two turnover's in it's  
frequency temperature curve. The one it operates at is the upper  
turnover.

The 200 KHz crystal is probably an X cut. It's frequency /  
temperature curve is parabolic rather than third order. Since it has  
only one change point in the frequency / temperature curve it is  
called an inflection temperature.

Strange but true ...

Bob


On Mar 30, 2007, at 10:09 AM, Francesco Ledda wrote:

> The temperature at which the Freq/Temp ratio is minimum is called the
> Crystal Turning Point.
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Cecil Acuff
> Sent: Friday, March 30, 2007 6:55 AM
> To: Phil M.; Bob Camp
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] 200KC calibration crystal source
>
>
> If I'm not mistaken the crystal oven for the 17Mhz crystal and the  
> 200KC
> crystal are not ovens that are turned off by the switch on the  
> rear.  The
> difference between these crystals and those in other radio's that  
> don't use
> ovens is in the design of the crystal.  The crystals in the 390A were
> designed to be operated at an elevated/controlled temperature to  
> perform
> properly....the ones in other radio's were designed to perform  
> properly at
> ambient....operate either outside those parameters and the
> frequency/stability changes dramatically.  A look at the stability - 
> vs- temp
> curves for the two types would reveal this quite clearly.  (I'm  
> sure there
> is some technical name for those curves...just don't know it)   I  
> do know
> that ovenized crystals have a long flat plateau in their curve that  
> once up
> to temp allows a fairly wide (relative) window of temperature  
> variance with
> little resulting frequency change.  Below that temp. you fall over  
> a knee in
> the curve and it's down hill pretty much for a long way.
>
> Just some thoughts...
>
> Cecil...
>
>
>
>
> ----- Original Message -----
> From: "Phil M." <pmills7 at houston.rr.com>
> To: "Bob Camp" <ham at cq.nu>
> Cc: <r-390 at mailman.qth.net>
> Sent: Friday, March 30, 2007 4:43 AM
> Subject: Re: [R-390] 200KC calibration crystal source
>
>
>>
>>>
>>> Taking the 17 MHz crystal out of the oven is not going to help the
>>> stability of the radio much at all.
>>>
>>
>> I don't think it will hurt the stability of the radio much at all  
>> either
>> for
>> typical swl and amateur.  It is used only on the bands up
>> to 8 mc.  Many other fine receivers are quite stable with none of  
>> their
>> xtals in ovens.  Many of us use our  R-390A's with the ovens turned
>> off anyway.
>>
>> thnks, Phil
>>
>>
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