Re: Need Formula for length of spiral

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

Your statement is well made. I was not looking at the size of an antenna,
This is a good posting. I was looking at the propagation velosity of an AC
signal on any conductor.  All coax venders list the velosity difference of the
coax they sell.You nead this to cut your cable.  A conductor is not free space
      Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Thu, 14 Feb 2002 16:53:41 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: Need Formula for length of spiral
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Thu, 14 Feb 2002 17:17:15 -0700
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> 
> 
> 
> Tesla list wrote:
>> 
>> Original poster: "rheidlebaugh by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
>> 
>> correction: The quarter wove length of a conductor is not the free space
>> quarter wavelength.IT is 6 to 15% less than free space controled by Z of the
>> coil or conductor.
> 
> 
> More properly, the dielectric constant (epsilon) of the surroundings. For
> all intents and purposes, air is epsilon=1. A thin coating on the conductor
> will slightly load it, but the effect is more one of loss (sigma) than
> speed (epsilon).
> 
> Also, don't confuse this with the "resonant half wave dipole length being
> shorter than free space halfwavelength" so favored by antenna builders, and
> alluded to in the 6-15% mentioned above.
> 
> Cutting an antenna slightly shorter than a half wave (or quarter wave for
> ground planes) is an expedient technique to get the feed impedance
> resistive (which improves the VSWR when feeding from the presumed resistive
> source).  An idealized halfwave has a feed impedance that is mostly
> resistive, but has a small reactive component.  The actual feed impedance
> is a function of not only length, but diameter, as well.
> 
> Any standard antenna textbook, like Kraus or Balanis, will cover this, and
> the formal derivation of it, in more detail than anyone could conceivably
> need.
> 
> 
>