Presentation on theme: "P. M. Livingston (Presentation from a few years back) An 80 meter Aerostat-borne Phased Array for Field-Day."— Presentation transcript:
P. M. Livingston (Presentation from a few years back) An 80 meter Aerostat-borne Phased Array for Field-Day
An optimized 80 meter end-fire array shows excellent front to back ratio Moderate soil conductivity; real high accuracy ground 18 radials, 10 meters in length Balloon support: 50 meters (155.7) high, centered between the antennae base Nearly 20 dB front-to-back ratio, end-fire. Pattern direction easily switchable by reversing the phasing line.
Proper phasing leads to a tremendous FB ratio Net gain: 2.65 dBi Front to back ratio dB Max lobe launch angle: 25 deg. Minor back lobe angle: 1`30 deg Average gain = 0.21 = -5.68dB If sum of radiation and loss resistance ~ 50 ohms, then radiation resistance = 10.5 ohms.
VSWR is acceptable for a 50 ohm match to the phasing line
Currents in the two antennae are well-balanced Curiously, the phase difference is nearly 100 degrees, not 90, as expected
Phasing line details Phasing line impedance: 75 ohms short length: 62.5 degrees long length degrees Actual lengths will depend on the cable velocity factors Frequency sweeps reveal that the pattern looses some of its front to back ratio for fixed length phasing lines but still remains better than 5 dB over the entire tuning range. At the 3.5 MHz end, the FB ratio is 5.7 dB and at the 4 MHz end, it is 6.2 dB
Thermostat wire for the antenna can be purchased at Home Depot Wire lengths: antennae: meters (68.6) of # 18 wire (Note: 50 meter suspension implies that the antennae wires make an degree angle with the vertical) Ground radial lengths: 10 meters (we use the radials for the present 160 phased array folded in half). Antenna wire is looped through an eyelet at the ground end. The antenna wires are tuned to the band ends or middle by changing the length of the loop by fixed amounts.