TopBand: 160M RF into Create RC5A3 Rotor Box

Mon, 8 Sep 1997 10:32:25 +0000

> From:          K1ZM@aol.com
> Date:          Mon, 8 Sep 97 05:19:08 +0000

Hi Jeff

> Thus far, I have tried the best ferrite beads I have on both the rotor cable
> right at the control box and on the A/C line cord of the control box - with
> absolutely NO EFFECT on the problem.

The beads might be only "half a cure".  RF is attenuated by having a  
low shunt impedance in conjunction with a high series impedance. 

The bead will add some series impedance (generally not much per bead, 
however), but no matter what that impedance is... the attenuation 
will be ZERO unless you have some shunt impedance at the load.

Think of the bead as a resistor and inductor in series for RF. The 
voltage drop across that resistor would be near zero, if the load 
impedance (the rotor box) was high compared to the bead impedance.

There has been stuff posted saying a certain bead has a certain dB 
attenuation, but that is incorrect. The attenuation depends greatly 
on the load impedance! 

What you may need to do is add small by-pass caps at each rotor 
terminal directly to the rotor chassis, and maybe even bypass the 
line cord to the chassis (if they didn't do that). 

Be sure to use the proper style of capacitor if you bypass the line.

.01's should do the trick, especially in combination with the beads. 
Just the capacitors alone worked with my rotors. The Create is pretty 
RF sensitive compared to a Tailtwister and such.

73, Tom W8JI

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