Antenna efficiency ?

[Andre Kesteloot]

Gang, interesting approximation of antenna efficiency and radiation resistance
André
*********************
G0MRF@aol.com wrote:

> [...]
>
> Over the coming weeks I'm looking forward to getting the Whitton ARG Church
> steeple antenna back in action. The 300 foot long wire is only accessible on a
> Friday evening. Although it loaded up perfectly on 73k, the practical results
> were poor due to high levels of night time noise on that band. 136kHz should
> be much improved.
>
> Incidentally, I wonder how close some stations are to 1 Watt ERP?  If my 300
> foot wire has an electrical length of 15 degrees, then its radiation
> resistance should be apx:
>
>   (15 x 15 )  / 312  =  0.727  Ohms.
>
> If maximum power transfer occurs with a 160  Ohm output matching transformer
> Am I correct in assuming that the efficiency of the antenna is apx
>
>   0.727 / 160  x 100%      or   0.454 %  efficient ?   i.e.  220  Watts RF  =
> 1 W ERP?
>
> This seems optimistic in the extreme, but it will be interesting to compare
> the wire with the known performance of the 12m high Marconi T from last
> weekends tests.
>
> 73.             David Bowman     g0mrf@aol.com