goofy frequencies

Here in the U.S. I'd suggest checking with Cal Crystal Lab / Comclok. They claim that "Custom frequencies - our specialty", they have no minimum order quantities, and on the one occasion I dealt with them I found them to be quite friendly to the small-shop developer. I've heard similar good things about them from some other folks who have used their services.

Oh, in this case, I agree. It's not hard to simply work out a problem like this by hand -- done it many times, myself. An efficient program using recurrences is more a demonstration of mathematical education than outright utility.

In this program's case, it illustrates to me that the author was somehow exposed to this recurrence method -- probably some reading at some point -- and wanted to embody it in an algorithm. Sadly, the author was not _also_ exposed to better numerical methods for actually computing the terms using a design by someone crafting around the limitations of floating point computations on computers. The line used to compute the next term, line 15, is very very poorly designed. It's straight out of "the book," so to speak. It's the very first way one learns to do it. But it is obvious the author was NOT exposed to good methods for computing terms. People like Bill Gosper know how to do this well, by the way, to drop a singularly important name in this area. The program author obviously hadn't much education on that side of the mathematical road.

So it is a case of selective education and showing off one side, without knowing much on another.

My point about a thorough grounding in recurrences and generating functions remains, though. And given this program's lack of skill in getting the most out of floating point, I'd recommend a good text on numerical methods, as well. One that deals with theory, not practice so much. One needs to learn to fish for themselves, not eat fish others catch for them.

Jon

Jan Crystals, Ft. Myers FL. Google for the web page.

Jim WX6RST

Toothpaste on window glass. Grind it a little too far you could bring it back up with a few lines of pencil lead (graphite).

Jim

FT-243

Jim

Another thing we like to do is to run DDSs backwards, at negative frequencies. You can do stuff like simulate quadrature encoders, or make polyphase motors run in either direction. That's easy in binary.

John

What's wrong with the likes of the Fox XpressO service?

Dave.

Nice! Thanks. And right here in Kahlifohniah, cool. For John and others who may be interested:

On Mon, 15 Jun 2009 22:19:02 -0400, Spehro Pefhany wrote: ...

"High school 'birdbath'"?

??? Rich

Yeah, that's an odd expression. Maybe he's from England?

Bob

What did you guys call these things? Or do you recognize them)

Best regards, Spehro Pefhany

Hmmm. Maybe it's a birdbath. Or, it could be a cotton candy machine.

I don't recall seeing any birdbaths in high school. A lot of birds (aka girls), but they wouldn't let us watch them take their baths in high school.

Bob

This

ftp://jjlarkin.lmi.net/Lap-Tech.JPG

is a 40 MHz oven-type vacuum-sealed glass AT-cut crystal that is made for us by Lap-Tech in Ontario. They mark the turning-point temperature on each one. These are superb crystals... high Q, low aging. They look like little pieces of jewelry.

John

Neet.

Glass? It would be much more poetic to use pure fused quartz. And a sintered quartz plug for the white part.

And, uh... non-stoichiometric SiO2 for the leads I guess???...

Oh well.

Tim

We had those in the metalshop and woodshops in Jr. High & high school. The called them 'institutional sinks'.

I've got some 1-1/2" long glass ones in the 100kHz range here that look very posh. And yeah, they were also sinfully expensive.

These are about $12.

John

Hand sink?

Cheers! Rich

I added a short DOS program (yes, it runs under WinXP and doesn't tie up the processor, when running -- it uses the multiplex interrupt to pass back unneeded CPU time to Windows) to display the convergents of continued fraction values. It includes a calculator feature and displays floating point notation, as well. Kind of a swiss army knife thing.

The ZIP simply contains the DOS exe file.

It shouldn't be too hard to use. But you'll need the DOS box. It will run on DOS-only systems and old Windows stuff, as well. Just a QB program. It's free to have, pass around, etc. If anyone wants the code, that's free, too. Just ask. It's a zero-order attempt, but seems to work modestly well.

Jon