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
>be happening:
>
>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
standing waves.
Here are some explanations for the phenomena:
W5DXP:
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-->
-----------------------////////////-------------------------
<--Iref-out <--Iref-in
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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