[R-390] Re: 200 KHz crystals again

[Bob Camp]

Hi

The crystals in the oven are specifically cut at an angle that gives  
minimum temperature slope in the vicinity of 85C. Dropping the oven  
temperature to 45C will make the oscillators significantly less  
stable. It will also walk them off frequency by more than just a little.

I'm not sure what is right with using the ARRL circuit and so bad  
with coming up with one of your own. I'm also not quite sure why a  
"free" cell phone TCXO is worse than one you pay for. If 1 and 10 MHz  
miniature TCXO's (not XO's) are out there free I haven't seen it ....

There have been a number of papers published on crystal reliability.  
Do a Google on "Frequency Control Symposium". A good library may have  
copies as well. I have not seen any that substantiate a *reliability*  
issue on crystals run at 85 versus crystals run at 45C. I also have  
not seen any indication of it in any of the work we have done.

Bob Camp
KB8TQ


On Jun 23, 2007, at 7:01 PM, Perry Sandeen wrote:

> Gentlemen,
>
> Wrote: > First you'd have to put three 455 crystals together and  
> somehow fuse them so that they
> became one crystal. Then you could grind off material to raise the  
> frequency.
>
> Asked: > Is it possible to disassemble an HC-6 crystal and grind it  
> to a different frequency?
>
> Wrote: > You could grind a 100K to 200K with some good lapidary  
> equipment.
>
> Wrote: >why not just come up with a little drop in to generate a  
> 200 KHz square wave off of a cell
> phone TCXO?
>
> I would respectfully offer that these cures are far worse that than  
> the disease
>
> IIRC I posted this a while back but I’m re-posting it as I believe  
> this is the path of least
> resistance to solving the 200 KHz problem.
>
> First though the true source of the problem.  The oven runs at  
> 85C.  This will always be a
> problem.  Finding a way to lower it to say 45C would go orders of  
> magnitude to keep both crystals
> running for probably an indefinite time.  The cure for this is  
> another rant.  Contact me off list
> if you want a simple heater ckt.
>
> A  Simple Solution.  (Purists close your eyes so you won’t be  
> contaminated)
>
> 1.  Obtain a copy of the ARRL handbook 2004 to 2006 , which are the  
> only copies I have.
>
>  2.  Go to section 25.15 (2006 manual).  There is circuit called "A  
> Marker Generator With
> Selectable  Output".
>
> 3.  Buy the PC board, 5 IC’s, a few miscellaneous parts and an  
> aluminum box. If you don’t want to
> buy the board RatShack has dual IC boards that can be used.  Build  
> unit. One can obtain 1 or 10
> Mhz TXTO’s very reasonably for a  master oscillator.  A side  
> benefit to using a TXTO is that one
> can slave the 17Mhz oscillator. Or one can use either a 1, 2, or 4  
> MHz crystal on the marker
> generator board.
>
> 4.  Set jumpers to any desired sub-multiple of  your choice. Inject  
> the cal signal into Pin 5 of
> 205.  The harmonics are probably strong enough that you won’t need  
> any amplification. If not
> increase the 20 pf cap to .001 mfd  or larger.  Then V205 and V206  
> become redundant.
>
>  Regards,
>
> Perrier
>
>
>
>
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