[TenTec] COAX AND FERRITE BALUNS

[AC5E at aol.com]

Hi All: 

A properly wound coax balun with the layers bucking is an extremely effective 
balun. I generally use RG213, and a 2" piece of 4" ID plastic pipe with three 
wire ties spaced equally around the inside and masking taped to it for the 
form.  

For 20 and up, I use four turns inside the pipe, tie them all very tightly, 
masking tape three more ties to the outside of the pipe, come out and wind four 
four turns outside. The second layer should be wound back across the inside 
winding,  don't pass the end of the wire through and wind the second winding 
over the inner winding. Tie the second winding and remove the form. Then tie and 
tape the heck out of the double bundle. 

For 40 meters I add four more turns, making three layers of four turns each 
or twelve turns in a "double bucking" winding.  For 80, I go with six turns on 
a layer, with a 3" long form, and go four layers, 24 turns total, with the 
same arrangement. 

Now - ferrites are fine, but it should be noted they won't take a lot of 
power. They reach their curie point and lose most of their choking ability at a 
fairly low temperature, and I have had some enclosed beads break with only 3-5 
watts of  reflected power. If you must use ferrites at the antenna make sure 
the 'tenna makes a fair match to the transmission line so you don't wind up with 
ferrite dust instead of a balun. 

The enclosed "winding on a rod" style also works well but some commercial 
current baluns can get hot enough to catch fire when there is a lot of RF on the 
outside of the coax. Yes, it's happened to me.  Don't let it happen to you, 
especially if the balun is where it might cause a house fire. 

And by the way, don't try to figure the actual impedance of a ferrite balun 
unless you have some means to isolate and measure the inductance of the outside 
of the shield. A conventional "clip the L meter across the ends and measure 
the inductance won't work" because  have a short, the inside of the coax, 
across the ends of the balun. The result is a drastically low reading that causes 
the unwary to dismiss them as a waste of time.  They aren't - they just take a 
little thought. 

Speaking personally, I use choke baluns at the antennas, and ferrites at the 
lightning arrestor and on the inside of the bulkhead. 

73  Pete Allen  AC5E