Antenna efficiency ?
Sat, 07 Feb 1998 08:42:07 -0500
Gang, interesting approximation of antenna efficiency and radiation resistance
> 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 firstname.lastname@example.org