490 MHz Vertically Stacked Crossed Dipoles (Interconnected with two Unequal Feedlines), analyzed using 4nec2 after Dimensions determined using nikiml's Python Optimization Scripts.
It was found to be a TRUE OMNI, with roughly SAME Gain on all Azimuths, but SWR was poor and would need an additional Matching Network or Quarter-Wavelength Impedance Transformer.
Horizontally Polarized Raw Gain = -1.5 dBi (+/- 1 dB) and SWR (50-ohms) = 2.0, which is right at limit for tripping the self-protect circuitry in some Transmitters, with no margin left to accommodate likely SWR degradations in the Feedline, construction inaccuracies and Proximity to Nearby Objects.
SUMMARY OF DIMENSIONS: [From 4nec2 File] Relem=5 ' Element Radius Gap=20 ' FEEDPOINT GAP (SIMULATED BALUN CONNECTION) VF1=0.66 ' Velocity Factor, Feedline to Top Dipole VF2=0.66 ' Velocity Factor, Feedline to Top Dipole ' Half-Length of Dipoles (millimeters) (Max Y-axis Coordinates): HL=152 ' Distance Dipoles are Above and Below Z=0 Axis (millimeters): Zd1=150 Zd2=250 ' Feedine PHYSICAL Length (IN METERS) to Top & Bottom Dipoles: L1=0.244 L2=0.400 ' Feedline Electrical Length (IN METERS) to Top & Bottom Dipoles: FL1=VF1*L1 FL2=VF2*L2 ' Characteristic Impedance of Feedlines to Top & Bottom Dipoles: Zc1=85 [75-ohm Coax is close enough] Zc2=205 [Non-Standard Value]
