Re: Portable antenna(s) #antennas #v6


Gordon Gibby
 

Hi Miken.....

Well, you see, those ends are separated in SPACE....and therefore in TIME.    Therefore the superposition of the signals from each end, at any other point, will have to take into account the different DISTANCE (and therefore TIME) from each end, and therefore the PHASES will be affected.

The simple answer is that there will be points where they add, and points where they subtract.   Exactly the same thing like when looking at the effect of the reflected wave off the presumed ground causes antennas to have lobes of maxima and minima in the elevation plane.     I think on one of the exam questions, one has to deal with the impact of various antennas being fed in- or out- of phase and separated by different distances.   AM radio stations do this to create a beam pattern to emphasize their signal in desired directions.   

I've been very effective with a 40-meter half wave antenna operated on its 2nd harmonic from a bus-stop, by the way!   Made some well documented great connections!    So yes, you do radiate quite effective power.

73,

gordon gibby kx4z


On Mon, Feb 17, 2020 at 11:23 PM zl1bnb <mdnewman.nz@...> wrote:
I have my doubts about the effectiveness of end-fed antennas when operated at even harmonics of the half-wave frequency.

Consider an end-fed 80 metre half-wave operated at 40 metres.  One end of the antenna will be radiating a field which is in anti-phase to the field generated by the other end, and surely this will cause cancellation of the emfs developed in in any incident antenna. 

Sure, the antenna can readily be matched, and it may be an efficient radiator, but the opposing fields will generate opposing potentials , causing cancellation.

Where am I wrong?

73 de miken,  zl1bnb

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