[Milsurplus] FT-241 surplus LF crystals chan - freq list ?

[Hubert Miller]

-----Original Message-----
From: Bob Camp [mailto:kb8tq at n1k.org] 
Sent: Sunday, November 12, 2017 7:28 PM
To: Hubert Miller <Kargo_cult at msn.com>
Cc: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] FT-241 surplus LF crystals chan - freq list ?

HI

Nope, the process is identical regardless of the center frequency. If you *are* going to do an LF lattice, you would do a crystal sort first. Back in the 50’s there wasn’t much choice of how to do it. Even the “big boys” did it very differently than it is done today. Computing has come a long way since then ….. The theory and the equations are still the same. You can play with them a lot easier today than you could back then. 

I’m not suggesting that building LF filters sounds like a lot of fun. It will be a bit painful no matter how you do it. I’m only saying that *if* somebody wanted to do filters, the crystals are still useful, even after 70 years ….. 

To the extent you find problem units, a wash (of the blank) in an etching solution (ammonium bi-flouride is popular) likely will help them out. There are papers on the how and why of this dating back almost to when the crystals were new (1943). 

Bob

> On Nov 12, 2017, at 10:02 PM, Hubert Miller <Kargo_cult at msn.com> wrote:
> 
> It sounds like you are talking about an HF filter using surplus 
> computer crystals. I was talking about something quite different, 
> which was the filter circuits published in the 1950s for using those 
> surplus LF crystals, with specific channel crystals picked out.  I am not actually  interested in getting into the crystal filters business, as I'm not going to be scratch building anything. But I'm sure it's fun, and it is interesting to read the procedures.
> -Hue
> 
> Subject: Re: [Milsurplus] FT-241 surplus LF crystals chan - freq list ?
> 
>> Hi
> If you are going to build a lattice filter, first step is to see what the biggest pile of crystals is (frequency wise).
> Next step is to set up a simple sort process to “bin” them by frequency. Once you have all that, you design the filter around what you happen to have. If this sounds bizarre ….. you haven’t been in the crystal filter business .
> “Enhancing” even a simple test set to get reasonable motional parameters is easier than you might think ….
> 
> The bottom line is that in this day and age of fancy computer analysis software, it is easier to fiddle the design than to fiddle the crystals. 
> 
> Bob
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