Phase Shift through a 75m Texas Bugcatcher Coil
 

Richard Harrison wrote:
Cecil. W5DXP wrote:
"Unfortunately, I must disagree (very slightly) with Kraus."

I had invited readers to the helical antenna pages of Kraus to support
my wave advance comparison to the progress of a threaded bolt. I had
looked at page 229 in the 3rd edition with its Figs. 8-8 and 8-9 or at
similar figures in an earlier edition.

Upon looking agin, I still believe the figs. support my bolt comparison.
In any case, I`d study long and hard before arguing with Kraus.

No doubt, your bolt comparison is valid when each turn on
the "coil" is one wavelength long. But what happens when
each turn is 0.006 wavelength? Do you reckon something
might change?

Hopefully, I am not disagreeing with Kraus. It appears that
the question is: Does Kraus' one wavelength per turn helical
antenna have the same VF as a 75m Texas Bugcatcher loading coil?

Kraus' own graph shows that if one varies the turn circumference,
the phase velocity is not a linear correspondence. I would suggest
that lack of linear correspondence occurs in the 75m Texas Bugcatcher
coil. We cannot tell what the exact phase difference would be at
0.006 wavelength per turn, but the trend seems obvious to me.
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Richard Harrison wrote:
Eureka! My 1950 version of Kraus has that Fig. 7-19 on page 193. It
shows propagation velocities found by several researchers as a function
of helix circumference.

Phase velocity is the velocity at which a point of constant phase is
propagated in a progressive (traveling) sinusoidal wave.

My 3rd edition, shows the lack of a 1:1 correspondence between
the circumference of a turn and the phase velocity of that
turn. If one projects Kraus' graph back to 0.006 wavelength
for the circumference of the coil, the lack of correspondence
should become pretty large, maybe even matching my reported
EZNEC results?
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Cecil, W5DXP wrote:
"---are standing waves electromagnetic waves?"

According to Tigertek they are not. Photons are massless at rest. They
cease to exist. Waves made of photons thus don`t exist if they are not
in motion. A real electromagnetic wave must be moving to exist. Check
out Tigertek`s fact of the day.

Best regards, Richard Harrison, KB5WZI

Phase Shift through a 75m Texas Bugcatcher Coil
 

Jim Kelley wrote:
I didn't quite grasp the purpose of your bolt comparison, Richard. The
only limits Kraus puts on helices is that they are helical - anything
between a flat single turn loop at one limit and a straight line at the
other.

My 3rd edition only shows coil circumferences between 0.6
and 1.5 wavelengths. But the relative phase velocity is
1.0 when the circumference is 1.1 wavelength and the pitch
angle is 5 degrees. If the relative phase velocity is 1.0
when the circumference is 1.1 WL, doesn't that imply a
change in VF away from a straight piece of wire?
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Richard Harrison wrote:
Cecil, W5DXP wrote:
"---are standing waves electromagnetic waves?"

According to Tigertek they are not. Photons are massless at rest. They
cease to exist. Waves made of photons thus don`t exist if they are not
in motion. A real electromagnetic wave must be moving to exist. Check
out Tigertek`s fact of the day.

I agree that there is a logical contradiction between standing
waves and electromagnetic waves. Too bad the people using
standing wave current for measuring phase don't realize that.
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Jim Kelley wrote:
"I don`t quite grasp the purpose of your bolt comparison, Richard."

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. How long it takes the signal to travel the length of the coil
depends on the length of wire in the coil as well as the velocity factor
of the wave on the wire in the coil. If it were not so, Terman`s
explanation of the traveling wave tube (TWT) would not be valid. But,
GTE Lenkurt gives a similar explanation in its "Demodulator" of the TWT.
They manufactured TWT amplifiers and surely knew how they worked.

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

Best regards, Richard Harrison, KB5WZI

Phase Shift through a 75m Texas Bugcatcher Coil
 

Cecil Moore wrote:

Jim Kelley wrote:

I didn't quite grasp the purpose of your bolt comparison, Richard. The
only limits Kraus puts on helices is that they are helical - anything
between a flat single turn loop at one limit and a straight line at
the other.


My 3rd edition only shows coil circumferences between 0.6
and 1.5 wavelengths. But the relative phase velocity is
1.0 when the circumference is 1.1 wavelength and the pitch
angle is 5 degrees. If the relative phase velocity is 1.0
when the circumference is 1.1 WL, doesn't that imply a
change in VF away from a straight piece of wire?

Hi Cecil,

The entire point of Richard's citation is that VF is a function of
pitch to circumference ratio. It explains the very thing that you
need to support your argument about phase delay across a coil. It's
what I meant when I said "I still think it would be prudent to explore
and understand the precise nature of the delay through the coil more
thoroughly before making too many assumptions about this."

Beyond that, I don't understand the question. Kraus is pretty
explicit. I didn't see much need to read between the lines. But all
I have to look at is the scanned version on the web that someone
posted a link to a week or so ago.

You should send Richard H. a fruit basket. Who woulda thought to look
under Helical Antennas. :-)

73, Jim AC6XG

Phase Shift through a 75m Texas Bugcatcher Coil
 

Jim Kelley wrote:
The entire point of Richard's citation is that VF is a function of pitch
to circumference ratio. It explains the very thing that you need to
support your argument about phase delay across a coil.

Does "circumference" mean the circumference of the coil or
is it the actual wire length once around the helix?
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

Jim Kelley wrote:
But all I
have to look at is the scanned version on the web that someone posted a
link to a week or so ago.

Unfortunately, it has been removed. Did you save it?
--
73, Cecil http://www.w5dxp.com

Phase Shift through a 75m Texas Bugcatcher Coil
 

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