[TowerTalk] Balun for G5RV

[Jim Brown]

On 2/1/2011 1:57 PM, DGB wrote:
> And is it acceptable to enclose them in a non-conductive enclosure Jim,
> even at high power (1500w)?  We can get ice 3" thick sometimes!

It depends entirely on the degree of imbalance in the antenna, and to 
some extent on the electrical length of the transmission line.  Greatest 
stress is placed on a straight through choke when there is significant 
imbalance. The strongest cause of imbalance is feeding the antenna far 
off center.  An antenna with fairly good balance (for example, where the 
only imbalance is non-symmetrical proximity to earth or to surrounding 
conductive objects would not cause much dissipation in the choke, even 
at high power. On the other hand, running high power into a strongly 
unbalanced antenna (like a Windom) would likely put enough common 
voltage across the choke to fry it, and putting it in an enclosure would 
make it more likely to happen, and to happen at lower TX power, because 
it inhibits heat transfer.

I agree with Jim Lux -- the primary concern is dissipation.

73, Jim K9YC