The ON4IQ 4m array
The antenna system
Main antenna is a stack with 4x PA5070-15-9BGP dual band (4&6) by YU1CF https://www.antennas-amplifiers.com/50-70mhz-dual-band-antenna-15-element-6m-4m-duo (15 el on a 8.76m boom) with full azimuth, PST71 rotator and elevation control with 36 ” actuator. Phaselines are 1/2” hardline , loss <0.25dB and tuned within 0.01%. A dual band power divider was constructed in 1/2" hardline. The main feed line is a 1- 1/4" coax , loss <0.25dB. Total loss antenna to rig <0,5 dB .Sloping ground gives me a take off angle lower than over flat ground. It serves also as a back up antenna for 6m.
Antenna central point is at 111m asl. The antenna H-frame is about 7m by 6.54m and made out of welded steel tubing. Weight is >150kg for the frame, and complete structure is >200kg. Estimated gain is over 18 dBi free space gain on 4 and 6 m.
SWR on the array is better than 1.1 for the range 70.0 to 70.4 MHz and better than 1.15 for the range 50.0 to 50.5 MHz. Phasing harnass was cut within 1mm precision. Plots taken on HP8753 network analyser. The return loss of the phasing harnass is better than -40dB.
Radio horizon
Radiohorizon is excellent and identical to the 4x9el array on 6m, almost 360° negative horizon giving massive ground gain and low angle take off. Just AZ 60°, a hill blocks to 0.6° elevation but hardly noticable impact.