w8jk.nec

zip contains tool for Antenna Modelling with examples

CM W8JK with 0.1 - wavelength sp., converted with 4nec2 on 29-mrt-06 14:37
CM 	W8JK
CM Originally designed by John Kraus, W8JK in about 1940, this
CM antenna has some interesting properties. It's characterized
CM by two closely spaced elements driven out of phase.
CM Although the fields from the elements don't fully reinforce
CM in any direction, gain is nonetheless achieved because of
CM lowering of the radiation resistance due to mutual
CM coupling. And lower it is -- note the feedpoint impedance
CM of only 4.74 - j19 ohms. Compare this to a single
CM element. The lower resistance results in heavier current,
CM hence greater field strength, for a given power input. The
CM difficulty is that system losses can quickly eat up the
CM gain. Making this antenna from #12 copper wire (try it --
CM and include wire loss) drops the gain about 0.65 dB, not
CM too bad. But great attention must be paid to losses in
CM matching networks. And losses rapidly increase in
CM significance as the spacing is made closer than the 0.1
CM wavelength of the example. When mounted low (0.25
CM wavelength for the example), W8JK-type antennas have a
CM lower radiation angle than many other horizontal antennas
CM due to the inherent lack of high-angle radiation. As an
CM interesting exercise, save the pattern for later
CM comparison. Then delete the second source, making the
CM antenna into a Yagi. Note the increased gain. Even though
CM the "takeoff angle" is higher, the Yagi gain is as good or
CM better even at lower angles. In addition, the feedpoint
CM impedance has increased to a much more manageable value. On
CM the other hand, the W8JK will retain its performance over a
CM much greater frequency range than the Yagi.
CE

SY freq=21.2	' Design frequency.
GW 1 11 0   0 0.25 0   0.466 0.25 9e-4
GW 2 11 0.1 0 0.25 0.1 0.466 0.25 9e-4
GS 0 0 299.8/freq		' All in WL.
GE 0

'LD 5 0 0 0 58000000	' Copper wires

EX 6 1 6 0 1 0
EX 6 2 6 0 -1 0
GN 0 0 0 0 13 5.e-3
FR 0 1 0 0 21.2 0
EN