On Thu,2/4/2016 5:35 PM, Wes (N7WS) wrote:
Even though we often refer to the output of the KAT500 (or any other device that normally connects to a coaxial line, the currents on the output should be equal and opposite - which is the definition of balanced.
Sorry, that is NOT the definition of "balance." Balance is defined by equal potential to the reference plane, which for most land-based antennas is either the earth or the chassis of the transmitter that feeds it, which is usually ground referenced.
Consider the currents between the center conductor and the inside of the shield for coax. They must be equal and opposite. It is the common mode current on the outside of the feedline that produces any unbalance.
No, the common mode current is the RESULT of imbalance. AND -- common mode current is present in two-wire feedlines when the antenna or the transmitter is unbalanced. In those 2-wire feedlines, common mode current is the DIFFERENCE between the current in the two conductors.
Note also that feedlines have wavelength, and both voltage and current vary along the line. The DIFFERENTIAL voltage and current vary as a function of the behavior of the line as a transmission line, with Vf being that of the line. The COMMON MODE voltage and current vary along the line as a function of the line's behavior as an ANTENNA, where Vf is determined by the insulation on the outer conductor(s), so is 0.98 - 0.99.
I laugh at those who attempt to measure current in both sides of a 2-wire line and think that what they have measured is the current at every point on the line. It is not -- it's only the current at the point you measured it, and it's only right there if your measurement technique is without error. Which ain't easy.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
