Pi Attenuator Help

[KSP]

Hi can someone point me in the right direction here please. I need to derive a formula to calculate the attenuation value of the attached attenuator. I have so far calculated the characteristic impedance Z0 to be 99.052ohm (correct me if I am wrong), so how do I calculate attenuation in dB using only the resistance. Usually I would do 20log(Vin/Vout) but how do I do it using just the resistances? Is there a way?

Cheers

[robrenz]

http://chemandy.com/calculators/matching-pi-attenuator-calculator.htm
formulas are below the calculator

[KSP]

but that formula states:

Att = SQRT(Zin/Zout) + SQRT((Zin/Zout)-1)

which doesnt work because if the impedances are matched then this essentially tells me SQRT(1) + SQRT(0) which is nonsense

Am I missing something?

[robrenz]

I read that formula is for the minimum attenuation

[KSP]

Ok well it seems the formulae are designed for unmatched impedances (as it says 'for Zin > Zout')

I bodged a few things together and I got an answer which resembled what the calculator told me so I am gonna go with that

I made that a lot harder than it should have been...