How to change accurately resistor values in RF attenuator?

[palesha]

accurate resistor values

I hv to replace resistors of very accurate values in RF attenuator. Kindly guide me how to change/modity values of resistors as desired.

 

[Fom]

Re: accurate resistor values

If there any capacitor inside of your attenuator?
If so they should connected as follows:
R1||C1 in series with R2||C2.

R2 and C2 consider input impedance of your oscilloscope or other equipment and may be they really don't exist in your attenuator.

If you want to change resistor you should change capacitor also

R1*C1 should be always equal to R2*C2.

In other word if you increase resistor by 2, you should decrease parallel capacitor by 2 also.

 

[palesha]

Re: accurate resistor values

Thanks for ur reply.
I want to make 78.6 ohm resistor. I took one 75 ohm resistor & started scrapping it till i got the value 76.8 ohms. This way i made the accurate resistors i wanted to replace the defective resistors.

 

[hackeron]

accurate resistor values

the same resistor will be different ohms in different frequency
In my expierience,you can use network analyzer to measure it,and then replace the same ohms in hte same frequency.
hope that it is useful

 

[designtech]

Re: accurate resistor values

if its really important you could keep trimming options inside the chip