[TowerTalk] Dipole fed with balanced line?

[Jim Brown]

On 1/16/2012 9:32 PM, Hank Garretson wrote:
> Antennas like this do not have to be precisely tuned.

Yeah, sort of.  But any antenna that looks like a very high impedance at 
the feedpoint is likely to result in a difficult to match impedance at 
the TX end of the line. SO -- a "good" length is one that is not an 
EXACT half wave, or an even multiple of half waves, at any frequency 
where you want to use it. It is that high impedance that makes it more 
difficult to match. A little time spent with a spreadsheet working the 
wavelength equation is time well spent.

It is also VERY desirable that the antenna be symmetrical, so that 
common mode voltage and current on the line is minimized, which in turn 
minimizes noise pickup on the antenna and RF in the shack. While common 
mode current can be greatly reduced by a good choke, high common mode 
voltage can fry even the best of chokes. THAT'S why unbalance is such a 
bad thing.

73, Jim K9YC