In the interest of academic accuracy couple of
corrections:
The term is Piezo electric.
A. M. Nicolson (correct spelling) worked for Western
Electric or at least they had the rights to his work.
W.G.Cady was a university researcher. Cady made his work
freely available to a number of potential licensees while
the patent was in process. Western Electric chose to
challenge the patent based on the earlier work of Nicolson.
However, after a long court battle it was decided that Cady,
while not first had a much more complete understanding of
crystals as applied to electric oscillators. It is Cady who
gets the recognition for the inventions. Another important
contributor was G.W. Pierce of Harvard who developed several
practical oscillator circuits using two terminal crystals
(Cady's original circuits used four terminal crystals). The
patent litagation of both Cady and Pierce with Nicolson was
very extensive but, eventually, both won out and Cady was
recognized as the orginator of the crystal oscillator
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
----- Original Message -----
From: "Richard Knoppow" <[email protected]>
To: "Neil M Califano" <[email protected]>;
<[email protected]>
Sent: Friday, September 16, 2011 5:32 PM
Subject: Re: [Drakelist] Changing crystal frequency
----- Original Message -----
From: "Neil M Califano" <[email protected]>
To: <[email protected]>
Sent: Friday, September 16, 2011 5:05 PM
Subject: [Drakelist] Changing crystal frequency
Someone I know used to write on crystals with a pencil
claiming the frequency could be changed. Is this true or
an urban legend, because graphite is crystalline?
Its true but not because pencil is graphite. A crystal
is a mechanical oscillator! The frequency is determined by
the mass and thickeness of the crystal along with the
"cut". Crystals are cut from large crystals which are
grown. the angle at which the crystal is sliced in
relation to its axis determines the mode of oscillation
and many other properties including temperature
coefficient. The nature of piezeo electric materials is
that they generate a voltage when deformed and will deform
if subjected to a voltage difference across the
appropriate face of the crystal. Anything on the surface
will influence the resonant frequency including the any
dirt. Old time crystals were simply blocks of crystal cut
to the right angle and placed loosely between two
electrodes. They could be varied in frequency a little by
the pressure of the electrodes and some crystal holders
were made with an adjustment to get a short range of
frequencies. Crystals can also be varied by abrasive
treatment or adding something to the surface to increase
the mass. A pencil mark does this. In the days when
crystals were quite expensive there were a lot of articals
in ham magazines about how to make your own. After WW-2,
when lots of crystals became available surplus, there were
numerous articles on how to convert military crystals to
ham frequencies and kits with the necessary abrasives were
sold.
Modern crystals are usually grown and are made with
cuts not known sixty years ago. For instance, its possible
to make a crystal with zero temperature coefficient over a
very wide range.
I have not done a web search for piezio electric
crystals but I am sure there must be a decent tutorial on
them.
There was some controversey about just who originated
the use of crystals for control of oscillators but the two
most likely were A. M. Nicholson and W.G.Cady, the latter
of Bell Labs. I think Cady got the patent but Nicholson
was probably actually first. Cady's application give much
more detail on how to make an actual oscillator, that is
probably why he was recognized as the inventor.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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