ok I'll look on udemy

 

Also I am going through a pdf. What I want to know is what qualifies as low frequency and high frequency?

 

in the spice simulation I made the dB attenuated from 4dB to 1dB

 

turns out I have already bought a crash course before and it has a 35min video explaining decibels and a link to the decibel wiki with these I'm sure I can get it sussed!

 

in the spice simulation I made the dB attenuated from 4dB to 1dB

That would be a 3 db attenuation.

 

so I have a question if:
p1 = 10dBm
p2 = 5dBm can you talk me through how to add them please!?

 

because in the example I have it shows me how to derive the dBm from a starting point p, and p is in milli-watts
but in the question at the end of the video it asks to add p1 to p2 and their units are dBm

I now know the difference between power gain and voltage gain and I also found out that the decibel scale is a logarithmic scale which defines the ratio of 2 quantities

 

power gain = 10 log (power/1watt)
voltage gain = 20 log (voltage/1volt)
is this correct?

 

Not quite. If expressing gains, the units do not matter. They are ratios.

power gain from P1 to P2 is 10 log(P2 / P1)
voltage gain from V1 to V2 is 20 log(V2 / V1)

since power is proportional to voltage squared, 3 db is twice the power whether expressed as a voltage or a power.
but 3 dbV is only sqrt(2) times the voltage. 6dbV is 2 times the voltage.

You graph for a filter is showing the dbV, so the 3 db point is where the voltage is 1/sqrt(2), or 0.707 times the unfiltered voltage.

 

I can't see where it says dbV or see the 0.707 number can you point me to it please!?

 

so I have a question if I want to sum decibel-milliwatts how please
p1 = 10dBm
p2 = 5dBm can you talk me through how to add them please!?

 

Not quite. If expressing gains, the units do not matter. They are ratios.
I get that part

power gain from P1 to P2 is 10 log(P2 / P1)
voltage gain from V1 to V2 is 20 log(V2 / V1)

since power is proportional to voltage squared, 3 db is twice the power whether expressed as a voltage or a power.
but 3 dbV is only sqrt(2) times the voltage. 6dbV is 2 times the voltage.
I don't get that part.

You graph for a filter is showing the dbV, so the 3 db point is where the voltage is 1/sqrt(2), or 0.707 times the unfiltered voltage.
I don't get that part.

 

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-5/series-r-l-and-c/
I cannot for the life of me work out how to add the impedance when consulting google it point me to this page can you help or direct me please?

 

Try this link. I think it gives a clearer explanation than your link in post # 33.
If you were tought physics at school you will probably have been taught this. (I was.)

Les.

 

I remember that I did a diploma and it covered this but I've not done it for years, thank you for the link!

 

ok thats much clearer, you find the sum of the series impedance by
sqrt (resistor)^2 + (XL - XC)^2
and the phase angle by
tan^-1 (XL - XC/ resistance)
now I want to find the
Current soure
I and phase angle
VR and phase angle
VC and phase angle
VL and phase angle

 

I think I have gone off topic but I'm doing a course in order and it says I need to learn these things before getting to Narrow (Single Frequency) Band Pass filters!

 

ok thats much clearer, you find the sum of the series impedance by
sqrt (resistor)^2 + (XL - XC)^2
and the phase angle by
tan^-1 (XL - XC/ resistance)
now I want to find the
Current soure
I and phase angle
VR and phase angle
VC and phase angle
VL and phase angle

can you link me to a page that explains how to calculate these please
I and phase angle
VR and phase angle
VC and phase angle
VL and phase angle

 

link

there might be some helpful hints https://demonstrations.wolfram.com/PhasorDiagramForSeriesRLCCircuits/#more
by https://www.google.com/search?q=phasor+diagram+calculator+interactive

 

Thanks