In a first order rc filter...?

[seyyah]

In a first order low pass rc filter what's the difference between the two:

1- R=10KOhm C=10nF
2- R=5KOhm C=20nF

as the product of the two examples are same? How must we choose the values or what to care?

 

[gevy]

It is important to know the following.
What is a source of a signal for the filter?
What is the receiver of a signal for the filter?
The real parameters of a source and receiver will change constant time of the filter.
For example, the output resistance of a source will be summarized with the resistor of the filter,
input capacity of the receiver will be summarized with the capacity of the filter,
input resistance of the receiver will reduce a signal.
The best variant is variant with the minimal influence of a source and receiver on parameters of the filter.

 

[seyyah]

So there are 3 parts:

1- Input or source
2- Filter
3- Ouput or load or reciever.

Do you say that filter's impedance should match the load's impedance and source impedance for max signal to noise ratio? How can it be or how is it achieved?

 

[SkyHigh]

First-Order RC LPF Filter is a passive filter.

Analysing DC:

In case 1, R is higher thus a larger voltage drop and R dissipates more power as heat. Vo across C is therefore lower than Vo in case 2.
In case 2, Vo is higher thus the load voltage is close to the input voltage, but this does not deliver more current. This is better for signal transfer and low power filter design.

Analysing AC:

Both cases offer the same Transfer Functions of the LPF, thus will have the same frequency response on the Bode Plot.

 

[markty]

So there are 3 parts:

1- Input or source
2- Filter
3- Ouput or load or reciever.

Do you say that filter's impedance should match the load's impedance and source impedance for max signal to noise ratio? How can it be or how is it achieved?

In my humble opinion, the impedance matching is used in transimition line application, not here.
I agree with gevy.