RadioBanter - View Single Post - Phase Shift through a 75m Texas Bugcatcher Coil

Richard Clark · May 10th 07, 12:42 AM posted to rec.radio.amateur.antenna

On Wed, 9 May 2007 17:27:47 -0500, (Richard
Harrison) wrote:

A coil is a coil whether it is used in a traveling wave tube or used to
load an antenna.

Hi Richard,

That seems to be hardly so at the frequency under consideration, and
the application being described. TWTs and antenna loads vary
considerably with regard to this conjunction you are rhetorically
drawing.

A coil, in the classic circuit sense, is dimensionless in the face of
wavelength employed. (Yes, there are dimensions of length, radius,
and pitch etc.; yet and all, these are infinitesimal in comparison to
the wavelength of the signal analysis. If you move to the arena of
dimension becoming a significant portion of wavelength, then calling
it a coil is simply descriptive, not prescriptive. That is, it looks
like a coil, but it could in fact act like anything (such as
transmission line or antenna) or as a coil (but this would be a rare
occurrence). Hence, a coil is not always like a coil when there is
enough baggage such as the legacy of coil meaning inductance alone.

Many writers solve this by calling the structure a helix - which is
exactly the term used by Terman. So, a coil is a coil, except when it
is an helix.

The velocity factors are surely a function of coil
dimensions as illustrated by the research results given by Kraus in
Fig.7-19 in the 1950 edition of "Antennas". The variation surprises me.
There is probably more research which explains such variations.

I rely on his work in the same volume of 1955 that you have. The
velocity factors seem to be the same irrespective of sources or
terminology.

Returning to your first statement (taken last, here):
My point was that the signal is guided by the wire on the coil and isn`t
instantly transported by induction from one end of the coil to the
other.
The notion of instantaneous current and inductance is anathema.
However, phase lag via coupling should be a trivial computation and
the debate becomes one of degree (figuratively and literally). To
this point (and through the many years) few seemed interested in
quantification that would endanger the appearance of lofty discussion.

73's
Richard Clark, KB7QHC