RadioBanter - View Single Post

October 10th 03, 10:42 AM

In article ,
says...
| I wish to make a master oscillator for the shack, and am considering
| cutting my own crystals in order to reduce ageing. Is there a source
| of raw material?

Yes, open up an old crystal if you really must consider cutting your
own crystals. It is a very tricky task, so practise on scrap ones
first. Any crystal cut, will then take lots of time to settle and age.
Far better to use an old crystal which has already achieved stability
'as is', rather than start the aging process off again.

|
| Also, for temperature compensation, I am considering the use of bi-metals.
| (I've never seen one, but what is the mechanism used in Oxley's
| Tempatrimmer?)
|
|

A good quality crystal in an oven which provides proportional
temperature control, rather than on/off switching is difficult to beat
once it has had an hour to settle. Even better is a double ovened
crystal. Old lab grade equipment is a good source for these.

If you really must have the ultimate stand-alone standard then rubidium
standards are coming onto the second-hand market at quite affordable
prices.

Another solution is to build a little gadget which derives a frequency
standard off-the-air, phase locked using a PLL. Suitable sources are
198Khz LW and slightly less accurate, the line timebase of a TV tuned
and synched to a BBC channel (15,625 hertz). This is what I have used
to check the calibration of my own instruments for the past 20 years.

You would probably need that latter item anyway, otherwise what would
you calibrate your own standard against?

--
Regards,
Harry (M1BYT)...

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