Calculate tuned circuits IN YOUR HEAD

[@greengrayradio1394]

Quick and easy rule! I have never heard of this, even as an EE and a ham for nearly 50 years who has built many circuits. You learn each day!

[@MirlitronOne]

Given the nature of practical radio circuits, e.g. with stray capacitances and inductances, such approximations are really much more useful than encouraging people to calculate values from formulae to a ridiculous number of decimal places. They would be much better taught in radio amateur exams, with the accurate formulations given rather less emphasis, particularly for those who struggle with algebra. A nice and timely reminder, Peter!

[@blacksmock445]

Back in the 1960s, before the advent of calculators, I sat several Telecomms exams, when working for the UK Post Office. They would often pose problems involving reactances of inductors and capacitors at audio frequencies. They often chose 1592Hz. This made the awkward 2pi*frequency term in the formulas into a round 10000. It saved a lot of time if you spotted this.

[@najroe]

this is the approach used for many of my circuits, calculate roughly then trim as needed after testing, strays can really mess with your calculations on some practical applications

[@acestudioscouk-Ace-G0ACE]

The beauty of this method is that it is easy to remember, Handy when you don't have a device or book to hand.

[@SergiuCosminViorel]

i can calculate, am licensed physicist and engineer, but i never thought this. Good idea!

[@charlesbrown980]

This really makes it easy to modify radio projects intended for AM to Shortwave bands.

[@godarklight]

Nice little trick, I've only made two tuned circuits so far and both times I used the NanoVNA to show the resonance rather than worrying about the exact numbers.

[@giovafra61]

Always very clear and very practicle. Grazie, Peter.

[@Steve-GM0HUU]

👍Good tip Peter, thanks. Recently, I was experimenting with some antenna traps. This would have handy to get in the right ballpark.

[@laythabdulwahab9498]

Very good way of calculation

[@mansurazeez2229]

Calculations made easy! TQ mate 👍

[@daveharveys]

Thanks Peter, very useful.

[@trevorwoods3367]

Very useful information. Thanks.

[@jordanclarke2996]

Thanks for the great video Peter, Fantastic simple rule of thumb super handy.

[@owenvinall9970]

Thanks Peter very useful info.

[@on4mgy_radioamateur]

Very informing and good to see, thank you Peter

[@VE6LK]

Excellent video (as always) Peter! The questions related to this on the Advanced or Extra exams are real head-scratchers --- until now! 73 de VE6LK

[@pablovalbuena3422]

Great rule. Thank you Peter. Could you explain how the different combinations of L and C vary the Q factor? Thank you

[@vk3ye]

Q is a bit more complex. It's not just L & C combinations - it's more to do with the quality of the tuned circuit elements eg absence of resistive losses in the inductor.

[@pablovalbuena3422]

@@vk3ye ok. Thanks you anyway.

[@kensmith5694]

The best estimate of Q is basically like this: Compute XL as 2*pi*F*L Find the resistance of the coil. Q = XL/R This only works with thin wire and without parallel resistances in the circuit. In real circuits, you often have the input impedance of a transistor loading the LC circuit and forcing the Q to a lower value.

[@pablovalbuena3422]

Thank you!@@kensmith5694

[@johnwest7993]

Handy tricks. Thanks.

[@kensmith5694]

BTW: It is often easier to multiply by 3 then divide by 10. The reason is that you just move the decimal for the factor of 10.

[@bullthrush]

Good tip, thank you.

[@WECB640]

Excellent.

[@Kangsteri]

Thanks!

[@M0NTVHomebrewing]

Very useful Peter. Thank you. 73 Nick M0NTV

[@cosmefulanito5933]

Without being able to specify the input and output impedance, these calculations are not worth much.

[@kensmith5694]

These are very useful tips. He is talking of hitting the resonance frequency in a simple LC having only one L and only one C.

[@cosmefulanito5933]

@@kensmith5694 A tuned circuit is useless without being able to connect to anything.

[@MidlifeRenaissanceMan]

Did you know that today is Pixie Day 7/23 (in freedom dates) In fact, it has been pixie month 7th month of 2023 7023 How could you / we have missed it ??

[@realjohnboxall]

"Freedom dates", that's funny.

[@MidlifeRenaissanceMan]

@@realjohnboxall well there’s freedom measurements and science measurements. So why not freedom dates. We busted out the pixies. Managed to blow one up, mod the other in such a way to kill the receiver and so a pixie built by a 9 year old made it on the air for 2 QSOs

[@DavidKerzel-k3k]

Great way to get a first set of values when armchair desigining

[@bill-2018]

Pixie Day? I had to look that up. I put my Pixie on 5.262 MHz. 350 mW out, worked 180 miles plus a SWL report from 220 miles in the Netherlands. G4GHB

[@MidlifeRenaissanceMan]

@@bill-2018 Best I did was Sydney - Brisbane with VK2TJ one sunny afternoon in 2020 Only made a 20Km NVIS to Blacktown from Kogarah (Sydney) Both were on Mag Loop antennas to beat the broadcast interference.