how to select the value of RF choke!

[aj_silverthunder]

what range of value of choke can i use to block RF from 80Mhz to 100Mhz from other part of the frequency.how do u calculate the value of choke that should be used to block RF from 80 to 100Mhz with a help of formula!please help me ,the last time!

 

[FvM]

An RF choke doesn't designate a frequency selective filter, just a an impedance above a certain application dependant level. You have discussed examples in your various other posts before.

What you request now sounds like a bandstop. The most simple bandstop would be a parallel resonant circuit tuned to 90 MHz (in case of a series connected filter).

 

[aj_silverthunder]

can u give me the formula to calculate it.pleaseeee

 

[penrico]

For the inductors, you can calculate the impedance as:

XL = 2xPIxfxL

So, if you use a 100uHy choke, at 80Mhz

XL=2x3.14x80E6x100E-6= 50240 ohm. The 100uHy choke will act as a series resistence of 50K at 80Mhz

For capacitors, the formula is : XC= 1/(2xPIxfxC)

 

[aj_silverthunder]

can a 50K resistance of the inductor can resist 80Mhz -100Mhz frequency!

 

[penrico]

Sure it can. I don't understand what is your doubt here.

 

[aj_silverthunder]

my doubt is that i want to calculate the value of the choke which can block 80Mhz RF signals from entering to the other circuit with a help of the formula!.like this " https://www.flickr.com/photos/aj_silverthunder/4140932373/ ".
so i need all u r help guys!

Added after 1 minutes:

and how can u know that a 50K inductive reactance can block 80Mhz RF signals!

 

[Freddybaby]

It probably won't block ALL of the signal, there are lots of factors such as leakage and parasitic effects that reduce the "blocking".

You can re-arrange the formula to solve for L or go here:

http://www.vwlowen.co.uk/java/hf-filt.htm

or here:
**broken link removed**

and plug in some values. You have to know the input and matching impedance as well.

 

[frankliner]

You should have an additional capacitor at the pin to insure the RF is minimized. What attenuation(A) do you require? If z1 is the impedance of the choke. Z2 is the impedance of the blocking cap. Then
attenuation = z2/(z1+z2)

with your givens and assuming attenuation of 60db or A=1000
C = (1/A -1)/4*pi*f^2*L

 

[aj_silverthunder]

can a 5uh inductor block 90Mhz signal

 

[betwixt]

aj_silverthunder - please read the wise advice you are being given.

Brian.

 

[aj_silverthunder]

Betty watch the reply by me in "sine wave generator" topic,best of luck!!!!

 

[karesz]

Oha!
Young & cheeky...:-(
I belief "a man" need other style pls.
K.