Well.. of course I am talking about conventional transmission lines.
These are spaced a negligable portion of a wavelength apart. As such,
the fields surrounding them completely cancel one another at all points in
space. Thats basic, classic transmission line theory.
I agree, and I said before, that if these conditions are violated (such as
wires a quarter wave apart that you mentioned) then this no longer holds
true. Also, if you interject a huge plate of copper or something like
that into the field, you will obviously affect it.
Finally, the line loss measurements you made, while fascinating, do not
prove that energy was carried in the field. Obviously some is of course.
But line loss is normally due to dialectric loss. And that is a function of
too many other variables to be discussed in this short note. I will comment
only that all those examples you mentioned were no doubt widely different
in their dielectric properties.
Regards,
Gary, AA2IZ
----- Original Message -----
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
To: "Gary Hoffman" <ghoffman@spacetech.com>
Cc: <tentec@contesting.com>
Sent: Tuesday, October 15, 2002 8:57 PM
Subject: Re: [TenTec] TWINCOM feedline ?????????????
> But a wide spaced line WILL radiate. Antennas are made of slightly wider
> spaced parallel lines, for example the Quad, where the spacing is
> quarter wave. The connectors top and bottom (if horizontally polarized)
> radiate perpendicular to the plane of the element, while there is a
> cross polarized lobe at about 45 degrees from the horizontal radiation
> lobe. That's because while the vertical conductors are OUT of phase when
> viewed from a position perpendicular to the plane of the wires, and so
> the field in that direction cancels, but then viewed from within that
> plane (e.g. parallel to the spacers), the radiation from those currents
> are NOT completely out of phase. They are not out of phase precisely by
> the phase angle of the distance between them. For the quad thats 90
> degrees. That's presuming that the energy is carried ONLY in the
> currents, that there are no accompanying fields.
>
> But I have some experimental evidence that much of the energy of a
> balanced line is carried in fields surrounding the line. Then changes in
> direction of the line tends separate field from the line (much as a
> G-line) as do intrusions into that field. I don't have measurements of
> that dimensions of that field. But here's how I noticed it. I was
> checking line loss by shorting lines and noticing the difference between
> forward and reflected power at 144 MHz. First I checked a length of
> RG-58 and the loss indicated was exactly the value listed in the tables
> of cable loss. Then I added a coaxial half wave balun and the loss
> increased. Then I added a length of K-200 heavy duty balanced line. It
> has a pair of 12 gauge or 14 gauge conductors spaced about 3/4" in an
> oval of polythylene. I shorted the end opposite the balun by folding the
> conductors together and soldering them. I suspended the line clear of
> metal objects. The SWR went way down indicating considerable line loss.
> Then I moved a large sheet of copper up against the short, and the loss
> went down to what I expected. That tells me that much of the energy is
> carried in the field surrounding the balanced line and interruptions in
> the line diretion will separate the line from the fields. That's
> radiation.
>
> 73, Jerry, K0CQ
> --
> Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> Reproduction by permission only.
|