Да,усиление слегка преувеличено
В NEC2 тоже:
Frequency: 50.3 MHz
Antenna environment:
FINITE GROUND. SOMMERFELD SOLUTION
RELATIVE DIELECTRIC CONST.= 13.000
CONDUCTIVITY= 5.000E-03 MHOS/METER
Source in wire N 4: Z=51.678 + j 1.141 SWR(50+j0)=1.04
Elevation angle: 4.0 deg
Max Gain: 18.21 dBi at azimuth: 0 deg, F/B: 30.00 dB
Azimuth angle: 0.0 deg
Max Gain:
18.21 dBi at elevation 4 deg
Ga H 20m.gif