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CDX, the model shows the new short Vector. I'm thinking they shortened it so that all of the currents would be productive as shown on the model. You're questions regarding 3/4 wave versus 7/8 wave are good and it's somewhat unclear as to what works best. Testing in the field that both Bob85 and myself have done indicated that a main radiator length above 3/4 and less then 7/8 wave provided the most gain in the far field. Modeling does show that when you go past 3/4 electrical wavelength that the tip of the radiator begins to radiate in the wrong phase.


Which brings us back to the question of how is it possible for a radiator to begin showing signs of deconstructive radiation in the opposite phase and still appear to show an increase in far field gain? As you point out the Vector design is not the only antenna to show this characteristic. The 5/8 wave ground plane has apparent issues with the phasing in the lower 1/8 wave. I believe it's more complex then to assume if the lower 1/8 wave is in the wrong phase it will equally cancel out an additional 1/8 wave of the 5/8 wave. There is not an equal cancellation as though they were two parallel conductors.


Most of us agree that the end fed 5/8 wave beats the end fed 1/2 wave any day. This pretty much undermines the theory that due to cancellation, only the top 3/8 wave is functioning as an active radiator on the 5/8 wave. When it comes to the Vector there are other variables to consider beyond the radiator length. As I suspected earlier, maximum far field gain is dependant on the top of the radials and loop lining up with the dip in current on the main radiator. This is the point where the phase inverts and requires shielding of the radiator below it from the cone.


I recognize I did not answer the question of how it's possible to extend the 1/2 wave to 5/8 wave with the bottom 1/8 wave of radiation in the reverse phase. That's going to take someone who knows more then me to explain fully. I do agree it is the case with more then one type of antenna.