An LC calculator

[Skywave]

Scenario: You need to determine the values of the constants for an LC tuned circuit which consists of a fixed-value inductor, a fixed-value capacitor, and a variable-value capacitor.
You know: The frequency-limits you want for that LC circuit and the 'swing' of the tuning capacitor.
Question: How do you determine the value of the fixed-value inductance and the fixed-value capacitor?

Answer: You can sit down with pencil, paper and a calculator (and plenty of time) - or use a suitable nomograph - or you can use the attached Microsoft EXCEL spread-sheet.
[attachment=9258]

I've run several sets of data through this and compared the results with other known-reliable sources and methods: I do not believe that there are any logical or mathematical errors. But if you do find any - please let me know!
Thanks.

Al. / Oct. 28, '13 //

[Aerodyne]

Thanks for this, Al. It looks useful.
Tony

[Skywave]

Glad someone thinks it might be useful.

A bit of history. It all began during my attempts to build an experimental Q-multiplier: the centre freq. was 100 kHz. I estimated that a freq. swing of ±3 kHz would be sufficient and I had a 5 - 100 pF variable capacitor available. A bit of elementary analysis established that that 'known data' would be sufficient to determine the value of the fixed cap. in parallel with the variable cap. and coil - and the inductance value of that coil, too. However, not only could I then see that doing the calculations the traditional way would be labourious and prone to error, but that there was a reasonable chance that one day I'd be repeating the arithmetic in some other design task. My first reaction (as usual) was to look around the 'Net (as you do: there's nothing I'm ever going to create that someone else hasn't already done ), but, surprisingly, couldn't find the appropriate tool. Anyway, I like EXCEL for things like this - you can customize the 'application' to your own tastes and needs. And unlike things on the 'Net', I won't find that one day it's simply vanished.

Al. / Oct. 28, '13.

[pwdrive]

I can't do excel on my pc, but no doubt Al's efforts are spot on.

Lawrence.

[camallison]

Lawrence, why not install Libre Office - it copes with most spreadsheets?

Colin

[Skywave]

I can't do Excel on my pc . . .
Lawrence.

Err, I'm not sure what you mean. Do you mean you don't have Excel installed, or that your PC can't cope with Excel? Or . . . ?
Maybe I can help in some way?

Al.

[pwdrive]

I don't have excel installed, will get round to it at some point.

Lawrence.

[Skywave]

O.K. Lawrence: now understood; thanks.

A little digression: a 'P.C.' is just that, isn't it? A Personal Computer, with the emphasis on 'personal'. For me, a P.C. without word-processing, a basic graphics application, comms. facilities and a spreadsheet prog. is not worth having. It all depends on what you wish to use your P.C. for: hence, 'personal'. Analysis, and sometimes even just for the sake of it, 'does it' for me: I become fascinated as to what the relationships are between the bits and pieces of a given 'something' that enable that 'something' to produce its intended result. Obviously, that 'something' could be something quite tangible - like a transistor amplifier or something that can only exist in the imagination. Also, having the tools to predict the likely outcome of a number of possible scenarios often saves a great deal of wasted time and faffing about. A program like MS 'Excel' is a great aid in meeting both of those objectives: I wouldn't be without it. I've been 'doing' electrical and electronics engineering all my life, so the need for analysis and prediction are ingrained in me: probably due to a mix of nature and nurture.

Just my hap'worth: each to his own, etc.

AL. / Oct. 28, '13 //

[Joe]

Of course what we now call PCs are far removed from what IBM came out with in 1982!

- Joe

[Skywave]

Indeed Joe, indeed. And to think that IBM management decided that the concept of a 'Personal Computer' would never be taken seriously, especially for business applications, and at best would be regarded as a 'sophisticated toy'! Having said that, in all fairness to IBM, their line of business was mainframe computers: a huge gulf between those two platforms. My earliest experiences with PCs date from approximately that era and I can just about recall the delights of X-Y Write, Wordstar, Supercalc and dBase. And green screens!
Happy days: PC maintenance was so much easier then and PC-DOS was far easier to live with than its effective predecessor, CP/M.

Al. / Oct. 29, '13 //