Tom Rauch wrote:
> Hi Gary,
>
>
>>A lot of people are under the impression that the higher
>
> the current in
>
>>a particular part of the antenna the greater the radiation
>
> from that
>
>>part.
>
>
> I'm under that impression, as are all the textbooks and
> modelling programs I have.
>
>
>>That is not the case. In the instance of a quarter wave
>
> length
>
>>antenna the current is highest at the feed end and lowest
>
> at the open
>
>>end. That theory should then say that only the lower part
>
> of that
>
>>antenna radiates and the top, high impedance part, does
>
> little
>
>>radiating. But all of that antenna shares nearly equally
>
> in the
>
>>radiation of the signal.
>
>
> Sorry, but I strongly disagree.
>
> It is a well established and accepted fact the open ended
> region of any linear conductor...be it a vertical or
> dipole....contributes very little to radiation. That's why
> we can replace the open end areas with hats or other forms
> of "current sink" and have very little change in pattern or
> radiation resistance.
>
> Basic physics tells us EM radiation is directly tied to
> charge acceleration, not voltage. There are significantly
> more charges moving in high current areas of the antenna
> than at open ends.
>
> This is why inverted L antennas are so effective as vertical
> radiators, and why there is very little pattern or radiation
> resistance change when the end of an antenna is bent.
>
> It all comes down to ampere-feet.
>
> 73 Tom
>
Radiation resistance increases along the length of an antenna. Higher
radiation resistance means less current for a given amount of power.
73
Gary K4FMX
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