On 12/12/2010 11:16 PM, Fred McKenzie wrote:
In article
,
Stuart Longland wrote:

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? Is it just frequency stability or
is there something more fundamental?

Stuart-

Michael's explanation brought back memories of my teenage years and
home-brew crystal controlled rigs.

A shorter answer is that a microprocessor crystal frequency may not be
critical while a radio crystal frequency may be.

It would be critical if you needed your transmitter to be on an exact
frequency. In your computer, it wouldn't matter much because no one is
listening! The only time it would matter is if the crystal frequency is
used to keep the computer's clock accurate.

Fred
K4DII
There is nothing wrong with microprocessor crystals, they are often made
to good tolerances, often 10ppm or better. There are only a few common
frequencies (not surprising many are a power of two, or a multiple
thereof), and the crystals are manufactured in huge numbers so they are
cheap (often around 50 cents each or less in small lots). Many hams
have built good IF ladder filters out of these rocks. You do have to
buy a few of them to find a matched set for the filter, but the total
cost will be a fraction of what a new filter would cost. Another thing
about these crystals is that they are often found in very small SMT
packages. I'm not sure that the smallest sizes work well in a ladder
filter though. The same goes for the 'tuning fork' version that uses
laser timed metal elements with a very small amount of quartz (I've
heard that high quality quartz is getting scarce and crystal makers are
looking at ways to use less).