# Measure Vo/Vi Over the Frequencies 1kHz/100kHz

#### ironasona

Joined Nov 12, 2020
53
How would i measure the Vo and Vi over the frequencies 1kHz and 100kHz , would i have to make a impedance table and compare the values between them and if one of them match that's the answer ? or is this completely wrong ? any advice would be helpful .

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#### ericgibbs

Joined Jan 29, 2010
16,389
hi iron,
E

#### BobTPH

Joined Jun 5, 2013
5,772
Do you mean measure or calculate?

Bob

#### ironasona

Joined Nov 12, 2020
53
How would i measure the Vo and Vi over the frequencies 1kHz and 100kHz , would i have to make a impedance table and compare the values between them and if one of them match that's the answer ? or is this completely wrong ? any advice would be helpful .
or not ? So i as asked to Measure Vo and Vi over the range of frequencies 1k to 100kHz

#### ironasona

Joined Nov 12, 2020
53

#### ericgibbs

Joined Jan 29, 2010
16,389
hi,
If you have been asked to calculate from 1Hz to 100kHz, what increments in frequency do you plan to use.?
E

You posted this.
and if one of them match that's the answer ?

#### ironasona

Joined Nov 12, 2020
53
hi,
If you have been asked to calculate from 1Hz to 100kHz, what increments in frequency do you plan to use.?
E
my English isn't the best what do you mean by increments you mean ,what formulas i would use ? 1/2*pie*f*C , 2*pie*f*L and for impedance Z=/R^2+(XL-XC)^2

i was think i would need to compare the reactance of or XL and XC and what number matched that would be the answer

#### ericgibbs

Joined Jan 29, 2010
16,389
hi,
Are you asked to determine at what frequency the absolute impedance of the Capacitor and Inductance are the same.??

E

#### ironasona

Joined Nov 12, 2020
53
my English isn't the best what do you mean by increments you mean ,what formulas i would use ? 1/2*pie*f*C , 2*pie*f*L and for impedance Z=/R^2+(XL-XC)^2

i was think i would need to compare the reactance of or XL and XC and what number matched that would be the answer
yes

#### BobTPH

Joined Jun 5, 2013
5,772
This is hopeless.

Bob

#### MrChips

Joined Oct 2, 2009
27,137
Are you trying to measure or calculate?

Calculate the frequency when the reactance of the inductor is the same as that of the capacitor.
Now use this as a center frequency.
Go back two decades in frequency and calculate the voltage across the resistor.
Step up the frequency until you are two decades above the center frequency.
Plot the graph of Vo/Vi vs frequency.

#### Papabravo

Joined Feb 24, 2006
19,300
How would i measure the Vo and Vi over the frequencies 1kHz and 100kHz , would i have to make a impedance table and compare the values between them and if one of them match that's the answer ? or is this completely wrong ? any advice would be helpful .
The way you would measure the transfer function is to have an AC sweep generator applied to the input and have a Magnitude/Phase meter on the output. You can calculate it by hand using a calculator or 4-place logarithm tables, and you can use a simulator to make a nice plot of the response. Since it is a second order system I would expect a resonance peak at some frequency between the limits, like where the impedance of the inductor is equal to the impedance of the capacitor.

IIRC the resonance is where:

$$2\pi f\;=\;\cfrac{1}{\sqrt{LC}}$$

#### ironasona

Joined Nov 12, 2020
53
Are you trying to measure or calculate?

Calculate the frequency when the reactance of the inductor is the same as that of the capacitor.
Now use this as a center frequency.
Go back two decades in frequency and calculate the voltage across the resistor.
Step up the frequency until you are two decades above the center frequency.
Plot the graph of Vo/Vi vs frequency.
Am trying to measure .Would i do the same thing if i was to measure it or would it be different ?

#### ironasona

Joined Nov 12, 2020
53
Are you trying to measure or calculate?

Calculate the frequency when the reactance of the inductor is the same as that of the capacitor.
Now use this as a center frequency.
Go back two decades in frequency and calculate the voltage across the resistor.
Step up the frequency until you are two decades above the center frequency.
Plot the graph of Vo/Vi vs frequency.
ok, thank you i think i know what to do now

#### Papabravo

Joined Feb 24, 2006
19,300
This is the result you should be aiming for:

#### ironasona

Joined Nov 12, 2020
53
ok, thank you i think i know what to do now
yeah thats what i was getting.

#### MrChips

Joined Oct 2, 2009
27,137
Am trying to measure .Would i do the same thing if i was to measure it or would it be different ?
What is the difference between calculating and measuring?

Calculation is applying the theory. It is predicting what one would expect from the theory.
Measuring is verifying and confirming the theory and the calculations.
Do both. They go hand-in-hand.