Topband: Chokes - ferrite vs air

[Gary Hinson]

Folks,

I've used home-brewed and commercial "QRO" ferrite choke 'baluns' before.  
With QRO and hi-SWR, they get warm, sometimes hot to the touch: I guess that's 
the result of choking off the power on the outside of the coax and/or 
saturating the ferrite.  With QROo. & extended cooking time, I expect the 
ferrite denatures and they cease choking anything.

Somewhere on the web*, I've read that air-core chokes are better: abt 6 inches 
of coiled coax wound neatly as a single layer (NOT bundled) on abt 4 inch 
diameter PVC pipe, or something like that.  Theory is that the air core won't 
saturate.  Best of all, they're practically free.

Anyone more knowledgeable/experienced than me have views either way?  Do 
air-core chokes work OK on 160?  How many turns & what diameter work best??

73,
Gary

ON/G4iFB

*  I can't remember where - maybe in W4RNL's collection of articles at  
http://www.cebik.com/radio.html  ?



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