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Frank,
Just to confirm we are both working on the same system, I have - Number of radials = 36 Length of radials = 10 m Diameter of radials = 2 mm Frequency = 7 MHz Antenna height = 9 m Antenna diameter = 1.64 mm = 14 AWG Ground resistivity = 150 ohm-metres Ground permittivity = 16 IMPORTANT: If NEC4 gives you the input impedance of the radial system I should be very pleased to know what it is. Otherwise we shall have no idea where the discrepancy arises - in the radial system or in the antenna efficiency calculation. Radiating efficiency is estimated by my program by the well-known formula - Efficiency = Rrad / ( Rrad + Rradials ) provided antenna and radials reactance are tuned out. Whereas NEC4 calculates efficiency by integrating power flow over a hemisphere WITHOUT tuning out antenna and radials reactance. Altogether different. ---- Reg, G4FGQ |
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