[TowerTalk] Ferrite Bead Balun Impedence Req'ts for Quad

[steve_lacourse at agilent.com]

I'm putting up a multi-band (20,17,15,12,10 & 6) quad antenna (2 el Gem spider quad) and will be feeding each band wire with a separate feedline through a switchbox (Ameritron). Each feedline between the switch & antenna will be a 1/4 wave stub of RG62 or RG11 cut to length. At each feedpoint, I intend to put a ferrite bead balun on the coax to help minimize wire interaction. 

While I think the right bead mix is #77 (or maybe #43) to suppress 10 - 50 MHz, what I don't know is how much impedence do I need and thus, how many beads to put on the line. Somewhere along the way, I read that the balun impedence should be 5x the load impedence. 

If the quad is at 100 - 130 ohms, should I design for 600 ohms of balun impedence? Why 5x and is this a valid rule of thumb?

73's
Steve KD7NTK