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Hi, center tap transformer, how to calculate?

michael1978

Mar 17, 2012
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Hi,
can somebody, explain me, HOW I HAVE TO CALCULTE this tapped transformer?
i have this site
www.zen22142.zen.co.uk/Theory/tunedcct.htm
i calculate Impedance for example of this circuit the total inductance, in serie with 1416n tapped 313n total round 1720n, there is 10.7Meg plus inductance 1720n = 115.636 Ohms, but this tapped inductance, how do i have to calculate to find imedance, with the same frequency, of other, THANKS...measure.png
 

Audioguru

Sep 24, 2016
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I never designed and built the IF transformer or discriminator for a radio, instead I simply bought an old one or took one from an old radio.

Two inductances in series have a total inductance that is their inductances added.
You do not know the amount of wiring or stray capacitance which affects the tuned frequency so the inductor is usually tuneable with a ferrite core that can be screwed in or out.
 

Ratch

Mar 10, 2013
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Hi,
can somebody, explain me, HOW I HAVE TO CALCULTE this tapped transformer?

Calculte (sic) what result? You have describe what you want to calculate.

i have this site
www.zen22142.zen.co.uk/Theory/tunedcct.htm
i calculate Impedance for example of this circuit the total inductance, in serie with 1416n tapped 313n total round 1720n,

The impedance between what two points?

there is 10.7Meg plus inductance 1720n = 115.636 Ohms, but this tapped inductance, how do i have to calculate to find imedance, with the same frequency, of other, THANKS...View attachment 42848

What component is 10.7 Megs? What imedance (sic) are we referring to now? What is "other"?

Ratch
 

michael1978

Mar 17, 2012
388
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I never designed and built the IF transformer or discriminator for a radio, instead I simply bought an old one or took one from an old radio.

Two inductances in series have a total inductance that is their inductances added.
You do not know the amount of wiring or stray capacitance which affects the tuned frequency so the inductor is usually tuneable with a ferrite core that can be screwed in or out.
Thanks man, but i will try to experiments...
 

michael1978

Mar 17, 2012
388
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Calculte (sic) what result? You have describe what you want to calculate.



The impedance between what two points?



What component is 10.7 Megs? What imedance (sic) are we referring to now? What is "other"?

Ratch
Hi Ratch, this is if amplifier, and i mean the impedance between 0 to 313nH, you measure with the same frequency center frequency 10.7MegHertz, for example two inuctors in serie between 0 to 313nH to 1420 is 1720(round) , and this total inductance 1720nH you have to find impedance with center frequency of 10.7MegHertz and that is 115.636 Ohms, but from 0 to 313nH i dont know how to find impedance……..:(
 
Last edited:

Audioguru

Sep 24, 2016
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The tuning capacitor is parallel with both inductances in series. The parallel LC resonates with a high impedance.
Since the LC resonates with a high impedance then the reactance of each coil is much less that the impedances in the circuit.
 

Ratch

Mar 10, 2013
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Hi Ratch, this is if amplifier, and i mean the impedance between 0 to 313nH, you measure with the same frequency center frequency 10.7MegHertz, for example two inuctors in serie between 0 to 313nH to 1420 is 1720(round) , and this total inductance 1720nH you have to find impedance with center frequency of 10.7MegHertz and that is 115.636 Ohms, but from 0 to 313nH i dont know how to find impedance……..:(

I still don't have a definitive two points from where you want the impedance. I will guess that it is the two red dots on your schematic. That makes it two parallel branches, one of which contains L1 and C2 in series and the other just C1 by itself. The calculation of the impedance is shown below. As you can see, there is no resistance component in the impedance and the reactance is 192.42 ohms inductive. If you want the impedance from a different location or need an explanation, just ask.

Ratch
michael1978.JPG
 

michael1978

Mar 17, 2012
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The tuning capacitor is parallel with both inductances in series. The parallel LC resonates with a high impedance.
Since the LC resonates with a high impedance then the reactance of each coil is much less that the impedances in the circuit.
Hi, i understand now...………..thnx
 

michael1978

Mar 17, 2012
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I still don't have a definitive two points from where you want the impedance. I will guess that it is the two red dots on your schematic. That makes it two parallel branches, one of which contains L1 and C2 in series and the other just C1 by itself. The calculation of the impedance is shown below. As you can see, there is no resistance component in the impedance and the reactance is 192.42 ohms inductive. If you want the impedance from a different location or need an explanation, just ask.

Ratch
View attachment 42885
Hi, thank you i understand now ;-)
 
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