[Elecraft] A Good Antenna Length?

[k3ndm at comcast.net]

Jim, 
What you say can be correct. However, this need not happen all the time. When common mode issues arise one of the problems is that the wrong type of balun was chosen. Voltage baluns suffer when the VSWR gets too high. What you really need to use on these types of antennas is a current type balun. They have less of a problem than do the voltage type. 

I use a Carolina Windom here. That means I use a voltage type balun at the feed point, deliberately causing radiation from the shield of the vertical section of feed coax. 18 feet bellow the antenna feed point I place a 1:1 current balun, an RF choke, to prevent common mode problems. I have not had problems with common mode currents with this arrangement, and it will work at higher powers than the 100 Watts I normally use so long as the baluns and coax are rated for the power level you plan to run. 

73, 
Barry 
K3NDM 

----- Original Message -----

From: "jim" <jim at audiosystemsgroup.com> 
To: "elecraft" <elecraft at mailman.qth.net> 
Sent: Saturday, July 5, 2014 10:24:19 
Subject: Re: [Elecraft] A Good Antenna Length? 

On 7/5/2014 2:05 AM, David Cutter wrote: 
> You might consider an off-centre-fed dipole with appropriate balun and 
> choke. 

Not if you're going to run power. An off center fed antenna generates 
high common mode voltage, which will fry even the best choke when 
running power. I wouldn't consider such an antenna at greater than 100W. 

73, Jim K9YC 
______________________________________________________________ 
Elecraft mailing list 
Home: http://mailman.qth.net/mailman/listinfo/elecraft 
Help: http://mailman.qth.net/mmfaq.htm 
Post: mailto:Elecraft at mailman.qth.net 

This list hosted by: http://www.qsl.net 
Please help support this email list: http://www.qsl.net/donate.html 
Message delivered to k3ndm at comcast.net