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Title: Conjugate Match - Link Antenna Coupler - Shunt Reactance Post by: aa5wg on October 09, 2011, 08:21:26 PM Hi to all: AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
My question is going to be about adding compensating shunt reactance at the antenna coupler and ladder line connection point (inductance or capacitance connected between left and right sides of the open wire feeder). (1) The ARRL Antenna Book (1954) says the maximum reactance along the antenna system (antenna plus ladder line) is at electrical 1/8th wavelength or 45 degree points. This maximum reactance value matches the characteristic impedance of the line in use i.e. 300 ohms, 450 ohms, 600 ohms etc. (2) The Antenna Manual by Woodrow Smith Editors and Engineers, Ltd. 1948 states the maximum reactance for the above ARRL example is also equal to the characteristic impedance of the transmission line (i.e. 300 ohms, 450 ohms, 600 ohms etc.) divided by half the VSWR expressed as an integer and not as a fraction. Example: a 600 ohm line has a VSWR of 6:1 would be 600 divided by 3 or 200 ohms. This is a huge difference, 600 ohms vs. 200 ohms. For 160 meters this translates to a 147pf shunt capacitor (600 ohms) vs a 442pf shunt capacitor (200 ohms). Which of the above two shunt references do you think is correct? Chuck |