[TenTec] It's getting cold. Perfect antenna weather for a OCF dipole

Jim Brown k9yc at audiosystemsgroup.com
Sun Sep 20 12:27:58 EDT 2015

On Sat,9/19/2015 11:54 PM, Rick - DJ0IP / NJ0IP wrote:
> If you want to run high power (more than 800w), you will need to glue two cores together.
> You won't find the coax I used, so use RG-142.


I hate to be a wet blanket, but off-center fed antennas produce VERY 
high common mode voltage/current, enough to fry a very good ferrite 
choke with as little as 100W.  Running a power amp is really asking for 

I now recommend using TWO 5,000 ohm ferrite chokes on well balanced 
dipoles running more than 1,000W.

The "coil of coax" chokes are simple inductors. If the length of the 
feedline makes the feedline capacitive, the choke will cancel part or 
all of the reactance of the feedline and the common mode current will 
INCREASE. Obviously, the extent to which this occurs will be different 
on every frequency. For this reason, a coil of coax makes a lousy common 
mode choke.

73, Jim K9YC

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