At 07:57 PM 11/21/2003 -0500, Joe Subich, K4IK wrote:
>Get off your high horse. In a series circuit, which a loading
>coil most certainly is, the current into and the current out of
>a device must be the same. In the RF circuit, if the current
>into and out of the coil is not the same only three things can
>1) there is radiation
>2) there is loss
>3) the measurement is disturbing the system being measured.
We are not dealing with closed circuit, but distributed and an antenna with
Here are some explanations for the phenomena:
The key to understanding is to realize that the net current is the
phasor sum of the forward current and reflected current (on a standing-
wave antenna). Assume a 10 degree phase delay through the coil on the
frequency of operation. Ifwd-in and Iref-out are on the same side of
the coil. Ifwd-out and Iref-out are on the other side of the coil.
Ifwd-in--> coil Ifwd-out-->
Assume that |Ifwd-in| = |Ifwd-out| which satisfies Kirchhoff
Assume that |Iref-in| = |Iref-out| which satisfies Kirchhoff
Ifwd-in + Iref-out = net current on left side of the coil
Ifwd-out + Iref-in = net current on right side of the coil
Ifwd-out lags Ifwd-in by 10 degrees
Iref-out lags Iref-in by 10 degrees (Iref-in leads Iref-out)
Now let's assume that Ifwd-in and Iref-out are in phase. So current
on the left side of the coil equals Ifwd-in at zero degrees plus
Iref-out at zero degrees which is a current maximum point.
Ask yourself: Can we have a current maximum point on both sides of
the coil? I trust that answer is obvious.
Ifwd-out lags Ifwd-in by 10 degrees. Iref-in leads Iref-out by 10 degrees.
So current on the right side of the coil equals Ifwd-out at -10 degrees
plus Iref-in at +10 degrees, NOT a current maximum point.
Therefore, in this example, net current on the left side of the coil
cannot possibly be equal to net current on the right side of the coil.
73, Cecil http://www.qsl.net/w5dxp
and summarized by W4JLE:
If we feed an antenna at the current point, the current decreases as the
voltage increases along the antenna element from feed point to end..
That being said, a coil replacing a segment of an antenna (in order to
physically shorten it) will exhibit the same properties (relating to
currents) as the segment it replaced.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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