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

[Jim Smith <jimsmith@shaw.ca>]

Steve,

It isn't the antenna impedance that counts.  There was a great thread on 
this topic recently.  Look in the archives for a lengthy thread started 
by K3LR with W0IYH in the title on 8/18/03.  You will find the answer to 
your 5x question as well as to many other questions you haven't asked yet.

73 de Jim Smith    VE7FO

steve_lacourse@agilent.com wrote:

> > 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
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See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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