# How to calculate R and C for Am Demodulation envelope detection?

#### Bilal12

Oct 22, 2015
3
Hello , one question if posible .

How can I calculate the value of R and C for an Am Demodulation envelope detection circuit.

Knowing that the carrier wave is 20KHz, 1Vpp, and the message signal is a 32Hz, 2Vpp, with a 5V DC offset:

and thank you.

#### Martaine2005

May 12, 2015
4,887
Hi Bilal12,
Firstly, I would cheat! As the equations turn my brain to mush!

I would stick a 1K and a 1nf to start. Or a varistor. And adjust the cap. Maybe 5nf 10nf.
But have a read of the books as the equations are all there.

Martin

#### Martaine2005

May 12, 2015
4,887
The equations were there too.
39nf and 5.1K

Martin

#### Bilal12

Oct 22, 2015
3
thank you for your replay . but who did you get c=39nf and r=5.1K

#### Martaine2005

May 12, 2015
4,887
Have you forgotten all the web sites you asked?

Martin

#### duke37

Jan 9, 2011
5,364
Your circuit looks very strange, shouldn't the ground terminal of the scope be connected to ground.
I would not know how to calculate the values but R needs to discharge C fast enough to follow the wave form. The DC offset will affect the discharge rate and may allow 100% modulation to be detected without distortion.

Oct 22, 2015
3

#### Arouse1973

Dec 18, 2013
5,178
I think if you started off with an RC of 5 times the 1/fm (modulation frequency) and see how you go. There is a lot of contention over what formula to use. So try this first and see how you get on.

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