help with some electronic terms

[Space Varmint]

Similar to what Space Varmint states...

Q = ω L / R = (1/r)(√L/C); where ω = ωo = cut off frequency

I.E. a RATIO of reactance to resistance.

A way to visualize it is...a cut off intensity of a slope; or how "drastic" the cut off slope is.
Similar to what Space Varmint states...

Q = ω L / R = (1/r)(√L/C); where ω = ωo = cut off frequency

I.E. a RATIO of reactance to resistance.

A way to visualize it is...a cut off intensity of a slope; or how "drastic" the cut off slope is.

It's funny what the term "Q" stands for, Quality Factor. Because sometimes we may desire a low Q, but does that mean it is low quality when it is the desired out come? Some applications for low Q would be in a PLL synthesizer when we want a broad range of frequencies or bandwidth. If the Q is high it will severely limit the bandwidth. It can be broadened by physically adding a resistor to the VCO's tank circuit thereby lower the Q as seen in kulela's formula. The other factor in limiting bandwidth will be the design of the low pass or "loop filter". Noise limiters will also degrade bandwidth. Some of the right kind of noise is desirable.

 

[owenpauljames]

That is pretty interesting. Although the philosophy for receiver performance has changed over the years. I do well remember the famous signal to noise spec. You hardly see it anymore. Now days the term is "dynamic range". It has been found that the single most important circuit or stage of a receiver is the receiver's first mixer. This is where you want to take care. After that, just make everything clean clean clean and if your first mixer is working right. You got a receiver!

I will attempt to sum up briefly what dynamic rage refers to. Though the mixer is used in conjunction with the local oscillator to select a particular frequency, what is actually happening is the entire band of frequency is in the mixer all at once. So when we speak "signal/noise" it may be the opposite result you are really trying to achieve. Because attempt to over amplify a signal, you are in effect amplifying the entire band of frequencies. That means that Joe's alligator station down the street will be amplified too. You do not want that because Joe's alligator station will over drive the mixer causing it to go into an over driven distortion mode where everything in the band inside the mixer will be modulated by his station. So now we have the modulation of the selected signal modulated by our friend Joe. This is the infamous spec IMD (intermodulation distortion). All ports in that first mixer are important. But you can now see that S/N can be very undesirable at times. Also a good post mixer amp will have allot of effect. You do not want any reflected or standing wave products coming back into the mixer for reprocessing.

Why are you talking about Radio?

The original question was
"4)if i have an Op-amp based filter, how do i calculate its SNR?"

I was just helping clarify a question. Is ulot even making a radio filter?