lcrf_mechanical_calculator

LCRF_Mechanical_Calculator

Copy of an email exchange which resulted in design and construction of a mechanical calculator

John, & others...

Your Log-Grid LCRF chart reference was key to the whole project.

1. Print the Log-Grid LCRF chart from an older ARRL Handbook, and then roll it into a tube.
2. Glue this chart to the outside of a plastic or cardboard tube who's circumference equals the chart width.
3. Add a clear plastic tube over the outside of your now tubular chart (it should rotate freely around the chart).
4. Draw a vertical index line on the clear outer plastic tube.
5. Add the reactance scale to this vertical index line (the scale from the left edge of the chart).
• Now, as you rotate the chart under the index line that line will indicate L and C reactance at any combination of frequency, inductance, and capacitance.
• The index line will also indicate the inductance and capacitance values that will resonate at index-line indicated frequencies.
• It will also tell you what frequency will be resonant at any combination of L and C...and what the reactance of L and C will be.
• You can use this tool to find the amount of L needed to resonate a particular frequency with any given C.
• You can use this tool to find the amount of C needed to resonate a particular frequency with any given L.

OK. I am happy now. :-D

John VK6JY...thanks very much for the assist.

Arv K7HKL

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Arv Evans wrote:

John

I had forgotten about those old Log-Grid LCRF templates. Yes, they do the same thing as my nomogram. Maybe that is a good place to start from in developing a slide-rule type LCRF calculator? At least it does add to the repertoire of available references and tools for the project.

I'm not sure if this is going to be possible, but it is an interesting mental exercise, and one that could result in a useful homebrew project if I can come up with a workable design that is easy to reproduce. One cycle of the log scale can be represented on a circular scale, but extending it to multiple log scaled ranges becomes a problem that would seem to require an auxiliary scale to represent multipliers. At that point the design becomes more a physical engineering problem than an electrical and theoretical one.

My original nomogram came from an old RSGB publication (I have a copy of that out-of-print RSGB Electronics Databook someplace around here but cannot lay my hands on it right now).

Thanks for reminding me about the LCRF log-grid charts. I can see already how they might fit into the scheme of things.

Arv

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JMY wrote:

Hi Arv,

Not something I have thought about much - nomogram construction - especially circular.

I wonder if you recall whence it came and if it might be possible to do a fresh hi-res scan of it.

I tried the ARRL H/Bs for 1963 (quaint old units) and 1987, to get the attached. Does it do it?

John-Y

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