Dears,

I think there is a typo in the attenuaters section at: http://www.allaboutcircuits.com/vol_3/chpt_1/7.html

in the "T-section attenuator" description, the equation for calculating Z: Z=RO + (R2 ||(R1 + Z))

I think RO should be replaced by R1

Thanks,
Basel

 

There is a problem, but it is with the designations. R0 is Rout, not R (zero). And RI is Rin, not R1.

Under this drawing...

Disconnecting the source and looking in to the right at VI, we need to see a series parallel combination of RO, RI, RO, and Z looking like an equivalent resistance of Z, the source/load impedance: (Z is connected to the output.)

Z=RO + (R2 ||(R1 + Z))​

The paragraph above the formula also seems to have a problem.

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OK, looked at it again. Changed my description of the problem.

I would change the designations to Rin and Rout, it would be much more obvious, and not be mistaken for numbers.

 

Thanks for pointing out the discrepancy.

This is the change I am making to the copy at ibiblio:

Disconnecting the source and looking in to the right at VI, we need to see a series parallel combination of R1, R2, R1, and Z looking like an equivalent resistance of ZIN, the same as the ource/load impedance Z: (a load of Z is connected to the output.)

ZIN = R1 + (R2 ||(R1 + Z))​

For example, substitute the 10 dB values from the 50 Ω attenuator table for R1 and R2 as shown in Figure below.

ZIN = 25.97 + (35.14 ||(25.97 + 50))​

ZIN = 25.97 + (35.14 || 75.97 )​

ZIN = 25.97 + 24.03 = 50​