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Re: Reality. Re: Medhurst self resonant frequency and nodality (fwd)



---------- Forwarded message ----------
Date: Thu, 18 Oct 2007 17:19:40 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Reality.   Re: Medhurst self resonant frequency and nodality (fwd)

  The winding of wire into solenoid changes the self resonant frequency.
  cf any good text on antenna engineering.

  Or a good ham radio book, under 'continuosuly loaded antennas'.

  Roughly: for long, skinny, closely wound antennas, ONE HALF wave
  of physical wire length 'looks like' 1/4 wave of straight wire.
  This is the measured reality.
  (To the extent that such arrangements are not commonly used as
   antennas, may need to dig a bit for the refrences.  Still: true.)"

	In addition to most antenna handbooks try just about any edition of "REFERENCE DATA FOR RADIO ENGINEERS", originally published by IT&T and most recently, I think I remember, by Howard B. Sams.  Good treatment of "helical antennas" and their various possible modes of operation.  Used a lot more than you imagine, both as the low frequency "long, skinny, closely wound antennas", either self-resonant or base loaded, as well as larger diameter and more widely spaced "helical beams" at VHF through microwave and operating in an entirely different mode.

	The Tesla coils we know and love are exceedingly short [compared to wavelength] versions of the first mode and are thus exceedingly lousy radiators.  Formula in RDFRE will show you how lousy.  Far more RADIATION [not capacitive or inductive coupling necessarily] at VHF from the leads between the spark gap and the primary.

Ed