T

#### Tam/WB2TT

- Jan 1, 1970

- 0

Dave said:Uh HUH. Okay. I do appreciate the help. I am currently working with a

big, clunky variable capacitor and some RF chokes, connected by wire and a

switch (to choose which inductor is in the circuit). Unless I am

mistaken,

my R is already quite low because of this. So I should ADD R to the

circuit?

Would it be best to have a 1:1 relationship between R and X(L)? Or should

I

go for 2:1, 10:1, or 100:1? My old textbook doesn't seem to cover

anything

like this. One more thing, are RF chokes okay for tank circuits, or

should I try something else?

Thanks much for the help...

Dave

[email protected]

Dave,

If you are at frequency F, X(L)= 2 x Pi x F x L, where F is in Hertz, and L

is in Henrys. So, at 8 MHz, for example, a 10 uH inductor has a reactance of

2 * 3.14 * 8E6 * 10E-6 = 50.24 Ohms. If you want the Q to be at least 100, R

has to be 50.24 * 100 = 5024 OR GREATER,

RF chokes are NOT OK for tuned circuits. They are specifically made to be

fairly low Q. I don't remember what your load was, but the gate input of a

FET is about as good (high impedance) as you can get. What is your

frequency, what Q do you want, and what is the load impedance. What are you

driving it from? that has an effect also.

Tam