Calculation of RFC for 100Mhz RF 10,7MHz IF Mixer?

[clsfox]

I need to use an RFC inductor in the following circuit:

**broken link removed**


How can I calculate its value? This is an 30Mhz RF 5MHz IF mixer.

Then I have to use one again for the same mixer working at 100Mhz RF 10,7Mhz IF. Will 1uH be enough? How can I justify the chosen value?

In the same problem one more question: How can I find the input and output admittance of the 2n2221A for 100Mhz and 10,7Mhz in order to calculate the new values for the mixer?

 

[Yahia Muhammad]

i think it's better to use higher than 1uH to get better blocking

 

[clsfox]

Is there any formula to justify the chosen value?

How big should it be to get sufficient blocking at 30Mhz and at 100Mhz in the second circuit?

 

[rogerynt]

Try bigger inductor e.g22uH. I used 22uH inductor for 21.4MHz IF and it's alright.

Rogerynt

 

[clsfox]

Try bigger inductor e.g22uH. I used 22uH inductor for 21.4MHz IF and it's alright.

Rogerynt

22uH for 30Mhz should be ok then. What about 100Mhz?

 

[VSWR]

The inductance of RFC should be selected for negligible loading of the node it's connected to. For example, if the node (left connection of the 43.5 uH inductor) has an impedance of 1 kohm at the frequency of interest, the reactance XL of RFC should be at least 5-10 times this impedance. This means 5-10 kohm in this case. The reactance is calculated as XL=2*pi*f*L.