Chris,

I’ll second Warren’s motion.The radiation efficiency of a 100-turn, 1-meter diameter solenoid (of any reasonable length/diameter ratio) at 100kHz is in the hundreds of nano-ohms, i.e. a very difficult starting point with respect to dissipative losses directly and indirectly associated with wire resistance and coil inductance. Radiation resistance of a solenoid scales with turns squared, but with resistance scaling directly with turns, large numbers of turns is not a reasonable approach for practical wire diameters.

The reactive field (induction field), which comprises most of the field (for a solenoid that is presumably a small fraction of a wavelength) does not suffer low efficiency, but reactive field strength falls by a factor of eight for (practically speaking) for every doubling of distance, starting near the aperture boundary. The reactive field strength 1km from a 1-meter diameter solenoid (properly oriented away from the null) would be 1E-9 that of the field strength near the aperture boundary.

Regards,

Jim AA5BW

From: [email protected] [mailto:[email protected]] On Behalf Of Warren Ziegler
Sent: Friday, October 25, 2013 3:50 PM
To: rsgb_lf_group
Subject: Re: LF: air solenoids