help with some electronic terms

[ulot]

I'ld like to know the meaning of some electronic terms and values

1)what does the unit dBuV really mean?

2) what does a filter Q-factor really mean, i mean its effect on filter performance

3) what does filter selectivity stand for.?

4)if i have an Op-amp based filter, how do i calculate its SNR?

 

[quixotron]

Well I ain't a filter guy but,

1: dB uV means that whatever signal level you're measuring is referenced to a uV. and since we are dealing with rms voltages, we need to to take 20 times the log of the ratio of your signal level to 1 micro-volt. Antenna engineers, like me, use these measurements to predict field strengths in terms of ERPs.

Example. S1= 1056uV therefore, S1 in dB uV = 20 * log(base 10) (1056 uV/1 uV) = 60.5 dB uV

2: To be continued...

 

[MacFeegle]

2) Bandwidth is equal to the resonance frequency divided by Q; (BW=f/Q). Therefore the higher Q a filter has the lower the bandwidth.

3) I believe a highly selective filter is called that because it passes (or blocks) a narrow range of fequencies, ie narrow bandwidth and high Q.

 

[rjvh]

Well I ain't a filter guy but,

1: dB uV means that whatever signal level you're measuring is referenced to a uV. and since we are dealing with rms voltages, we need to to take 20 times the log of the ratio of your signal level to 1 micro-volt. Antenna engineers, like me, use these measurements to predict field strengths in terms of ERPs.

Example. S1= 1056uV therefore, S1 in dB uV = 20 * log(base 10) (1056 uV/1 uV) = 60.5 dB uV

2: To be continued...

What is ERPs ?

Robert-Jan

Yes i did look in wikipedia but still have a question mark, maybe a more simplistic explanation will explain it for me

 

[ulot]

thanks for the tips but what about measuring signal to noise ratio?

 

[mneary]

To measure SNR, terminate the input with no signal, and measure the output. This is the noise. Then apply a signal. This is the signal. The ratio (20 log(Vn/Vs)) is SNR.

This does not take distortion into account which would be SINAD.

 

[Externet]

Hi.
dBuV :
- dBu means voltage based decibels unloaded or unterminated; that is, with no reference to impedance, and the reference is 0.7746 Volts RMS.
- dBuV means the same unloaded voltage based decibel but with a one volt RMS reference instead of the 0.7746 V RMS.
That is, 0dBuV = 1 volt RMS ; 0dBu = 0.7746 V RMS

Do not confuse u for unterminated with µ for the micro symbol. If is not written as dBµV; is dBuV as for unterminated, not microVolts.
If you were unable to write dBµV in your question and you truly meant decibel microVolts, 0 dBµV = 1µV

Q is for 'quality' , believed to be the the best the least resistance an inductor has in its winding

Selectivity is the sharpness of the curve a filter circuit provides, being capable of passing or rejecting a frequency without affecting or being affected by other nearby frequencies.

Miguel

 

[ericgibbs]

What is ERPs ?

Robert-Jan

Yes i did look in wikipedia but still have a question mark, maybe a more simplistic explanation will explain it for me

hi R-J,
Its Effective Radiated Power.

https://www.electro-tech-online.com/custompdfs/2008/08/radiated.pdf

https://uk.search.yahoo.com/search?ei=utf-8&fr=slv8-&p=effective radiated power

 

[Space Varmint]

Q = Xl / R that's inductive reactance divided by resistance.

 

[Kryten]

Iv got a filter "book" by TI that I will post when I get home from work.. (I couldn't find on ti web)

 

[Kryten]

I didnt find the TI one but i have a couple of others about filters..

Here you go

 

[Space Varmint]

I didnt find the TI one but i have a couple of others about filters..

Here you go

By Golly I cannot save them. That sucks!

You wanna hear one of the great tragedies of my life...I took a 1 & 1/2 year correspondence course from Nat'l Radio Institute before I went back to school. It had a huge section on "Attenuators,Equalizers & Filters". This thing showed you how to break down a filter where you could analyze every arm & leg impedance in a complex latter network. I had my books stored at my folks house and neglected to pick them up a couple of years. Well they decided to remodel the basement and it was only one or two small boxes, and instead of calling me, they just took it upon themselves to throw my books in the garbage. Heart breaking story. I still love them though.

 

[neon]

I'ld like to know the meaning of some electronic terms and values

1)what does the unit dBuV really mean?

2) what does a filter Q-factor really mean, i mean its effect on filter performance

3) what does filter selectivity stand for.?

4)if i have an Op-amp based filter, how do i calculate its SNR?

1] means uv ratio in decibels it is a measurement it can be modulation ratio or other ratios.
4] you cannot calculate the SNR it is a spec given for a device to inply the maximun SNR it can achieve. It will vary form IC to IC inclusive variation of its own family.
2] as explained below is sharpness of the filter response.

3] filters ca be designed to pass and/or block frequency by design therefore the term selectivity.

 

[Kryten]

Found it

Hi i finally found the TI amp thing

 

[PhillDubya]

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.

Imagine graphically a high pass filter, with the side's slopes increasing of decreasing. Increase in slope, = increase in Q; conversely, decrease in slope, = decrease in Q.

 

[BaCaRdi]

Sure you can, need to save a copy, the original can't be edited without the acrobat writer(what ever is named now).

-BaC

By Golly I cannot save them. That sucks!

 

[BaCaRdi]

Ouch..know all about that!
just replace your mother with my ex-wife

no wrath like...you know the rest

Being a network engineer you could imagine all I have lost, in designs alone. Yep the computer an my laptop went with the rest of my stuff, written and digital storage alike.

-BaC

By Golly I cannot save them. That sucks!

You wanna hear one of the great tragedies of my life...I took a 1 & 1/2 year correspondence course from Nat'l Radio Institute before I went back to school. It had a huge section on "Attenuators,Equalizers & Filters". This thing showed you how to break down a filter where you could analyze every arm & leg impedance in a complex latter network. I had my books stored at my folks house and neglected to pick them up a couple of years. Well they decided to remodel the basement and it was only one or two small boxes, and instead of calling me, they just took it upon themselves to throw my books in the garbage. Heart breaking story. I still love them though.

 

[kulela]

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.

 

[owenpauljames]

To measure SNR, terminate the input with no signal, and measure the output. This is the noise. Then apply a signal. This is the signal. The ratio (20 log(Vn/Vs)) is SNR.

This does not take distortion into account which would be SINAD.

Thats a good way of mesuring signal to noise. but the equation is the other way round (20 log(Vn/Vs)) will give you the noise to signal ratio. (20 log(Vs/Vn)) will give you signal to noise.

Sorry if im being a bit pedantic.

 

[Space Varmint]

Thats a good way of mesuring signal to noise. but the equation is the other way round (20 log(Vn/Vs)) will give you the noise to signal ratio. (20 log(Vs/Vn)) will give you signal to noise.

Sorry if im being a bit pedantic.

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.