Design and Production of Bridge-T Attenuator (600 ohm) -1

I write article about Design and Production of Bridge-T attenuator (600 ohm)
I made this attenuator in year 2006.
Bridge-T attenuator circuit is shown below

For 600 ohm input and output impedance, value of R1 and R2
is calculated as folowing
R1=R*(10^(G/20)-1)
R2=R/(10^(G/20)-1)
Ｇ:Attenuation（dB）
*1）＊means multiplication,　/ means division,　^ means exponentiation
I used “Seiden 56SG” rotary swich with 34 steps for attenuation.
Maximum attenuation is 74dB, using E24 series of resistors
I show the result below.

Attenuation curve and impedance

Impedance error is within 3.7%
This time I wrote about designing part, next time I’ll write about actual production
*2) In case you want to make Bridge-T attenuator, then you can use folowing formula to calculate Resistor value
R1=R*(10^(G/20)-1)
R2=R/(10^(G/20)-1)
change R into circuit impedance value that you need, input attenuation level in dB (positive value),
Copy and paste the right side of equation into Excel cell ,then you can get result.
But resistors that have exact value are not exist. You have to choose closest value resistor from E24 or other series.