On 9 May 2007 23:29:28 -0700, Jim Kelley wrote:

On May 9, 3:27 pm, (Richard Harrison) wrote:
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

Ok. But what I was asking is what does any of that have to do with a
bolt?

The travel of one turn of a point at the radius (helical distance) in
relation to the travel of the same point in the depth (the linear
displacement after 360 degrees of the turn) is related to pitch. A
simple mechanical relationship. This is the bolt.

The signal flowing in the helix modulates a beam traveling within the
axis of the helix to impose its frequency upon it
(amplification/oscillation) through the pitch. This is the TWT.

The helical distance is supposed to express the linear completion of
the truncated 90 degrees of a quarterwave radiator. This is for the
loading coil.

There is no obvious correlation between the mechanical description,
the harmonic relation of the TWT and the degree relation of the
loading coil beyond the simple, visual metaphor which doesn't really
add any quid-pro-quo.

What is missing for the TWT is the necessary correlation of the beam
drift velocity which is wholly lacking from the bolt metaphor.

To say that the coil replaces the missing degrees of the truncated
quarterwave has likewise been so sloppily handled in the past, that
60-70% error brushed aside to prove equality provokes "so what?"

73's
Richard Clark, KB7QHC