[ARC5] Crystals Update

[Roy Morgan]

On Jul 17, 2009, at 8:27 PM, Michael Tauson wrote:
...
  a way to
> use a grid dip meter to check crystal activity.  The problem is I
> can’t remember how it’s done.

Set up a crystal socket with a short loop of wire, say an inch in  
diameter.  Couple the GDM to the loop and scan for a dip.  If you need  
relative activity, fix the loop with respect to the GDO coil firmly  
(and maybe variable) and notice the depth of the dip.

To test raw crystal blanks, simply balance the blank on the GDO coil.   
You can rest it on top of the horizontally oriented coil, or lean it  
up against it. You'll find the dip.

In both cases, tuning is going to be sharp. You may also find spurious  
exitation modes where you get a response at a frequency not the  
fundamental of the crystal.

>  Can anyone point me in the right
> direction to finding this again?
>
> Second, we all know that the thickness of a crystal has a direct
> bearing on its frequency but lost in that same echo chamber is any
> reference to the effects of changing the other two dimensions.

As you change the thickness, the activity can/is maintained by keeping  
the  blank's other two dimensions in proportion to the original.  So  
if  you grind a blank up in frequency, it may help to take a bit off  
the edges more or less equally to keep the activity up. Etching seems  
to dod this naturally.

>  Oh, and the asylum called to let me know my room is ready.  :-)

Oh good. Is your room equipped with some ammonium fluoride and  
suitable heater and wax container?

  Roy Morgan
k1lky at earthlink.net
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Groton NY, 13073
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