Posted by
N2EY on
Aug 12, 2006; 10:32pm
URL: http://elecraft.85.s1.nabble.com/Up-conversion-tp392867p392899.html
In a message dated 8/12/06 12:40:53 PM Eastern Daylight Time,
[hidden email] writes:
> It wasn't just crystal filters that improved. The older methods of
> computing component values (Image Parameter) was replaced by modern
> network theory in the 1950's and '60's and LC filters became a lot
> better performing as a result.
Excellent point!
Yet it was at that exact time that amateur designs were moving away from LC
filtering (such as the 50-60 kc. second IFs of receivers like the Hallicrafters
SX-88/S-76/SX-96/SX-100/SX-101) to HF crystal filters. The move to
transceivers and matched receiver/transmitter pairs (Heath SB line) may have had an
effect, too.
I'm not sure of the exact dates when it was first done, but by the mid 1960s
the use of computers to do circuit simulation and calculation was mainstream
in electronic design. Such design tools probably had an effect in that many
"paper designs" could be tried out in a short time, particularly for things like
filters..
>
> I don't see the widespread cheap availability of crystals with Q > 1
> million as likely to emerge without a major demand and some considerable
> advances in the materials available, as the present devices seem to do
> the job required.
>
Agreed. The main filter in the K2 uses selected microprocessor crystals and
some varicaps, yet gives very good CW performance and multiple bandwidths. By
comparison, one can easily spend half the cost of a basic K2 (or more) on a
couple of packaged CW filters for an HF IF. For VHF? I don't want to go there.
> There's an interesting article "The Design and Performance of
> Ultraprecise 2.5-mc Quartz Crystal Units" by A. W. Warner from the
> September 1960 B.S.T.J. discussing crystals with a Q of 5 to 6 million.
> You can read it at
http://www.ieee-uffc.org/freqcontrol/warner.pdfIncredible stuff from almost a half century ago.
But to get that high Q, they went to pretty fancy methods, icnluding vacuum
mounting. However, they were probably using natural rather than synthetically
grown quartz.
The things I find most disheartening were the aging curve and the fact that
they were using the 5th overtone to get to 2.5 Mhz.
>
> Now, if we could obtain a few dozen of those at 45 MHz, we would have
> something indeed.
>
I can imagine the size and cost!
73 de Jim, N2EY
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