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.
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Reg, G4FGQ