[time-nuts] The 5MHz Sweet Spot

Bob Camp lists at rtty.us
Sat Nov 2 09:12:55 EDT 2013


Hi

All the numbers I gave assume you are starting from a 3rd / 5th at 10 MHz. 

Bob

On Nov 2, 2013, at 1:30 AM, David McGaw <n1hac at Alum.Dartmouth.ORG> wrote:

> This all seems to be forgetting that the crystals are usually operated at 3rd or 5th harmonic.  The crystal in a 10811A is 10 MHz/3rd overtone.  A high quality 5 MHz/5th overtone crystal is really a 1 MHz fundamental, a large piece of quartz.  Running at a harmonic greatly reduces the influence of the package.
> 
> David
> 
> 
> On 11/2/13 1:07 AM, Bob Camp wrote:
>> Hi
>> 
>> The real answer is that nobody knows. The economics essentially make finding out very expensive. Q most certainly goes up, I don’t think anybody disputes that. The questions about flicker / ADEV all revolve around small blank parts with major edge sensitivity issues. They also probably were not running in a very good oven. Unless somebody with very deep pockets decides they need to find out, it’s going to be an un-answered question.
>> 
>> Bob
>> 
>> 
>> On Nov 1, 2013, at 11:41 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
>> 
>>> 
>>> On 11/1/2013 8:28 PM, Bob Camp wrote:
>>>> HI
>>>> 
>>>> If you doubled the diameter of the blank each time you cut the frequency in half, all sorts of nice things might happen. If you start with a 1/2” blank in at 10 MHz that goes to 1” at 5 MHz and 2” at 2.5 MHz. Around 1 MHz you would get to a 5” blank.
>>>> 
>>>> Good luck finding high grade quartz bars to cut 5” (or even 1”) blanks out of. You are going to have to go back to the autoclave fixtures at the very least. Since growth is (at best) linear you cost of quartz will scale with the size of the blank. I’d bet it scales a bit more than that if you want to keep the material at a high level of performance.
>>> You've explained the excuses vendors give for not making full
>>> size crystals.  But the question is, given these realities,
>>> does this reduce the theoretical advantage of the lower frequency
>>> and by how much?
>>> 
>>> Rick Karlquist N6RK
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