Assiming there is no tuner or feedline loss would linear loading a short doublet antenna increase performance?
My doublet it 68 feet long. It is used on 80 through 20 meters. Would linear loading make any improvement in performance on 80?
Assuming there is no tuner or feed line loss, the linear loaded 68 foot doublet antenna (with the tips coming almost all the way back to the feed point) will have more losses in play. Think about it, you have twice the material in the air, so losses will naturally go up, plus a loading method, and all loading methods including linear loading add loss to an antenna. The radiation pattern will be the same, however, so no change there.
However, once you get past the added losses, a good question to as is are those losses a bad thing when comparing the complete antenna system? Lets add one more detail and factor back in the feed line losses.
In the case of the straight 68 foot doublet, SWR comes out to something like 1030, however, on the linear loaded doublet (like the one I described above) SWR is closer 35. However, factoring in the feed line losses, assuming 100 feet of LMR400, an SWR of 35 will have about 49% losses on the 80 meter ham band, while an SWR of 1030 will have more like 97% losses. This is definitely an antenna you would want to use ladder line with, unless you have a remote auto-tuner at the antenna's feed point, in which case, tuning an SWR of 35 is much easier and more efficient than tuning an SWR of 1030, and that is even if the auto tuner has an SWR range of 1030 to begin with...
To get the SWR and antenna losses data, I used modeling. To get the coax losses for a given SWR I used
this page.
Another concern is moving the current maximums lower to the ground on the higher bands or causing RFI.
In what way do you see the current on the antenna getting closer to ground, is it more than a straight wire tied up to two end points?
The DB
