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Old 17th Mar 2023, 9:54 am   #1
Malcolm T
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Default Inductance and resonance calculators

How accurate are these on line calculators for determining coil inductance and resonant frequency of LC circuits ?.
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Old 17th Mar 2023, 10:27 am   #2
PsychMan
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Default Re: Inductance and resonance calculators

In my experience, they seem pretty accurate. Though, there are a lot of different ones out there.

I've used the LC resonance calculators to determine values needed for a resonant loop antenna. I've added enough turns to match the inductance (based on a meter reading), and sure enough, i've been able to tune to the frequency I want.

I really should just learn the maths myself though!

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Old 17th Mar 2023, 11:12 am   #3
Craig Sawyers
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Default Re: Inductance and resonance calculators

Depends on the frequency. But in any event the on line calculators are na´ve, in that they do not take account of inductor self resonance, and circuit Q.

The Radiotron Designer's Handbook 4th Ed is excellent for real world design rules.

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Old 17th Mar 2023, 12:36 pm   #4
Malcolm T
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Default Re: Inductance and resonance calculators

HF only , Bearing in mind there are going to be +/- errors in of the shelf components ie capacitors to add to the mix but most likely even more in home brew coil winding i suppose the best that can be hoped for is "close"
Thanks for the book suggestion.
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Old 17th Mar 2023, 3:05 pm   #5
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Default Re: Inductance and resonance calculators

Would this be of any help?
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Old 17th Mar 2023, 3:21 pm   #6
GMB
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Default Re: Inductance and resonance calculators

This site has loads of useful info on it: https://www.g3ynh.info/zdocs/magnetics/part_1.html
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Old 17th Mar 2023, 11:14 pm   #7
Malcolm T
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Default Re: Inductance and resonance calculators

Yes thanks very much for these texts , the math,s is a bit above my head, however i find it very interesting reads and am sure there is something in there to help.
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Old 17th Mar 2023, 11:30 pm   #8
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Default Re: Inductance and resonance calculators

Malcolm. How accurate do you need to be ?. The online calculators I use are my "go to". I am often making resonant circuits, my maths are diabolical.. There are trimmers and variable cores to make anything resonate at the required frequency. I bought a tray of 100 5 pin 10x10 mm inductors "toko type"... and I know or can easily guess the number of turns required. Abacs are/ were very useful in the day but my "go to" is the PC.
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Old 17th Mar 2023, 11:58 pm   #9
Phil__G
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Default Re: Inductance and resonance calculators

Anyone remember ETI's free slide-rule with inductance & capacitance scales?
Mine must be here somewhere, cant imagine I'd throw it away...
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Old 18th Mar 2023, 12:38 am   #10
Bazz4CQJ
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Default Re: Inductance and resonance calculators

Whenever I've used the online calculators, they've seemed fine to me. Useful for verifying any spreadsheets I've produced myself. But I am only using them as a hobbyist and on the sort of equipment that falls comfortably within the scope of this forum.

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Old 18th Mar 2023, 8:43 am   #11
Malcolm T
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Default Re: Inductance and resonance calculators

Wendy
Im not looking for microwave accuracy, just wanted to know if they were reasonably accurate , i,m in no doubt that they all are.
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Old 18th Mar 2023, 8:52 am   #12
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Default Re: Inductance and resonance calculators

Quote:
Originally Posted by Kentode View Post
Would this be of any help?
I have the third edition, only 7/6.....

Inherited from my Dad.
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Old 18th Mar 2023, 10:02 am   #13
regenfreak
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Default Re: Inductance and resonance calculators

The online calculator is accurate for VHF and VHF frequencies but how it is applied may introduce errors. All inductors have dustributed capacitance and self resonance frequencies SRF. The inductance of inductor increases as the frequency approaches the SRF and it behaves like a capacitor above SRF. The impedance peaks at SRF. The spaced windings of Toko coils are to mimimise the distributed capacitance between windings and to increase Q.

If you measure an inductor using 10khz, 100khz or 200khz of your LRC meter and measure the resonance frequency of a parallel LC tank circuit with a capacitor of known value. The predicted resonance frequency from the online calculator can be very different from the measured value if the resonance frequency is fairly close to SRF. The indicated inductance from resonance frequency measurement can be corrected if you measure SRF using a nanoVNA with shunt or shunt-through methods.
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Old 18th Mar 2023, 1:02 pm   #14
DrStrangelove
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Default Re: Inductance and resonance calculators

I downloaded a pdf of said Radiotron 4th Edition.

Turns out I have the reprinted dead tree version upstairs.

Who'd have thunk?
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