Active Filter: Bessel
(2st order, 12 dB/octave, Highpass)

2nd order Bessel Highpass

C=4.7n-10nF
Ra=1.1017/(2*pi*Fc*C)
Rb=1.4688/(2*pi*Fc*C)

Units: Rx [Ohm], C [F], Fc [Hz]