inductive reactance!how to calculate value of RF choke?

[aj_silverthunder]

inductive reactance!

guys how do u calculate the value of the rf choke using the inductive reactance formula, XL = 2∏fL .for example here u can see a schematic which transmits in a frequency 100Mhz,there u can see a choke!
my friend gave me this way to find out the value of choke
" 10kΩ inductive reactance would be fine.
That translates to
XL = 2πfL
10kΩ = 10000Ω
10000Ω = 2π(100M)L
L = 10000 / (2*∏*1e8)
L = 1e4/ (2*∏*1e8)
L = (1/6) 1e-4
L = 0.16e-4
L = 16e-6
L = 16µH."
so there fore the vakue of the choke should be 16μH.
but can u guys please tell me how did that 10kΩ come from.how did he take the 10KΩ from the circuit! please help me!

 

[svhb]

Re: inductive reactance!

The choke is used to filter out the 100MHz content in the power supply to the low frequency amplifier T1/T2.

To make a filter, you need always at least two impedances, here the choke together with R8 is the first one, C4 is the second one.

The value of the choke needed depends on how much you need to decrease the 100Mc ripple on the power supply.

For example, if you need -60dB (1000 times less on the LF side than on the HF side), Zc/((Zl+R8)+Zc) must be 1/1000. (Zc is the impedance of the capacitor, Lc is the impedance of the choke, google for the formulas if needed).

Be sure you use a capacitor that has not too much parasitic behavior on 100MC.

Stefaan

 

[aj_silverthunder]

inductive reactance!

i just wanted to know where does that 10k come in that formula.10K is the inductive reactance.

 

[aj_silverthunder]

so there are two impendance.the choke 10K and the resistor has 470 ohm and the other impendance is the c4 capacitor! should the capacitive reactance should also be calculated and compared with the first impedance,am i right!