[Antennas] Loading of dipoles and off center loading of dipoles

[Pat W]

>> I am using a 66' dipole, center loaded with 57.5 feet of 450 Ohm ladder
>> line fed with a 1:1 ferrite bead balun of RG58. and about 20 more feet
>> of RG58 to the transmitter.  I built this from instructions without
>> questioning anything about the construction.  It works fine.
--------------------------------------------------------------------------
>> But here comes the question...............  What the hell is the ladder
>> line for on the center loaded dipole?  I assumed it was to match the
>> impedance of the center fed dipole to the 50 ohm coax, but I now find
>> that the center of the dipole is ALREADY 50 ohms or there abouts, so
>> what is the ladder line for?
>>
   It appears that someone gave/sold you what could be called a short
G5RV. IT is a  1/2 wave dipole on 40m, with 1/2 wavelength of ladder line.
Unfortunately, the ladder line is 1 wavelength on 20 m.
(A standard G5RV has 1/2 wavelength of line on 20m, which is
approximately 1/4 wavelength on 40m).
The 1/2 WL of ladder line on 40m means that the load impedance
is the same on both ends of the line, ie 50 ohms.
The same is true on 20m.  However, since the dipole is 1 wavelength
long on 20m and the feedline is also about 1 wavelength long,
the very high impedance is presented on both ends of the feedline.
On a standard G5RV, the 1/4 wavelength of line on 40m transforms the
very high impedance at the antenna end to a very low impedance at the
rig end.
  You could experiment with different lengths of ladder line that
would present resonable matching to you tuner, instead of just
going with the length you are using now.
-- 
Regards - Pat W0OPW