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Old September 8th 08, 01:46 AM posted to rec.radio.amateur.homebrew
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Default Heterodyne conversion crystals

On Sep 7, 2:43�pm, Michael Black wrote:

Nobody has ground their crystals from scratch
since about the 1930's,
if even then. �I've been licensed since 1972 and in all the time
since
then I've never seen anything about it, not in magazines and books
going back to the late 1940's and not in more recent material.


There were articles in QST in the 1920s about cutting and grinding
your own crystals from the raw quartz, making holders, etc. A lot of
work and specialized equipment. The market was such that the
specialists quickly took over in the early 1930s.

After WW2 the enormous amount of surplus dominated the amateur market
for decades. Many of the "new" FT-243 crystals we bought were actually
surplus holders with new crystal inside.

�I do
recall the 1964 article in QST about a buy in SOuth America who
made his own tubes.


There's a guy in France doing it today. Has a movie on his website.
But again, lots of work and specialized equipment.

Go back far enough, and hams just needed crystals within
the band.
They had relatively little need for exact frequencies.


Well, yes and no.

Some xtal frequencies were more prized than others, because the
harmonics fell in higher bands.

I suspect even if the Handbook did give such details at one time,
little bits may be lost since when something is current, "everyone
knows" things that may not be obvious to someone who comes
later.


That's true of many things. Reading older radio books and magazines
can require knowledge of a lot of the jargon and methods of the day.

Now, they need them on exact frequencies, and they want them in
nice small packages, none of those FT-243 ones that were held
together with pressure.


The big difference is plated electrodes vs. pressure electrodes.
FT-243s are capable of quite good accuracy; .005% was common, which
works out to 200 Hz at 4 MHz.

Pre-WW2 xtals were big and rugged, but used a lot of quartz. Radio-
grade natural quartz came almost exclusively from Brazil, and the
difficulty of supply caused US xtal makers to develop xtal designs
that used less quartz. The FT-243 was ultra-miniature in its time!

73 de Jim, N2EY
 
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