RE: LF: air solenoids

["hvanesce" <hvanesce@comcast.net>]

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: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Warren Ziegler
Sent: Friday, October 25, 2013 3:50 PM
To: rsgb_lf_group
Subject: Re: LF: air solenoids

 

Christoph,

    A while back someone on the US longwave reflector posted the result of an experiment. They took a receiver to the site of a high power Tesla coil operating at LF, I believe it was being driven at 175kHz. they expected to hear it at some distance but were surprised to find out they could only hear the Tesla coil at very short distances. It seems that a coil by itself is an extremely poor radiator at LF!  It is unknown to me if there was any earth connection to the Tesla coil, perhaps only through the mains connection.

 

73 Warren

 

 

 

On Fri, Oct 25, 2013 at 4:20 PM, Christoph Schumacher <chris-schum@t-online.de> wrote:

no, cylindrical coils

Am 25.10.2013 22:11, schrieb Graham:

toroidal ?

 

From: Christoph Schumacher

Sent: Friday, October 25, 2013 8:53 PM

To: rsgb_lf_group@blacksheep.org

Subject: LF: air solenoids

 

Dear all,
is there anyone who was concerned sometime with the self radiating properties of single layer air solenoids without any piece of antenna wire?

73 dl7saq, Chris

 

 

--
73 Warren K2ORS
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