Design emission (harmonics)
If you know anything about impedance dividers and the transmission line inductance, capacitance and thus Zo, this is a low Q LPF, easily simulated. For say 220 ohm UTP.  Approx. 1~2uH/m &amp; 35pF?? /m. Depending on cable.

DO you know Zc(f)=1/(2pif*C) and when series R= Zc(f) it is at half power and when R=9Zc(f) it is Zc/(Zc+9R)= 1/10th the input V or 20dB down or -20dB.