Home brew six meter three element quad

 

The three element cubical quad antenna is an excellent choice for six meter contesting and other weak signal work, particularly if you want to be able to dismantle and transport the antenna.

Most quad designs call for equal spacing between elements. As the great antenna guru L. B. Cebik, W4RNL, SK, demonstrated, that is far from optimal element spacing.  The three-element quad described here is slightly modified from Cebik’s design to modestly improve SWR and free-space gain.  A calculator using Cebik’s formulations is available online. The free-space gain of my version is 9.55 dB, slightly more than the 9.34 dB gain from the Cebik model, and my version has an impedance at resonance of 50.1 ohms vs. 55.6 ohms for the Cebik calculator.  At 5 meters above ground, it delivers a calculated gain of 14.68 dBi at a takeoff angle of 13°, nearly ideel for Sporadic-E work. Far field plots are shown below; the horizontal plot is based on a slice of the field at !3°, illustrating the excellent gain, front-to-back-ratio, and side lobe suppression that make for an outstanding contesting antenna.  Even at relatively low antenna elevations, the main lobe of the vertical plot is less than 20° elevation.  (As a side note, Cebik’s model for a four element quad appears to offer a poor tradeoff between performance and size; the added element gives only 0.8dB additional gain, but almost triples the boom length from 2.4 meters to 8.9 meters.)

                 


Performance Data with Antenna positioned 6 meters above ground:

50.000 MHz  Z: (49.382 - i 5.148)    I: (0.0200 + i 0.0021)     VSWR(Zo=50): 1.1:1

50.100 MHz - Z: (50.445 + i 0.440)    I: (0.0198 - i 0.0002)     VSWR(Zo=50): 1.0:1

50.200 MHz - Z: (51.511 + i 6.073)    I: (0.0191 - i 0.0023)     VSWR(Zo=50): 1.1:1

50.300 MHz - Z: (52.580 + i 11.758)    I: (0.0181 - i 0.0041)     VSWR(Zo=50): 1.3:1

50.400 MHz- Z: (53.657 + i 17.503)    I: (0.0168 - i 0.0055)     VSWR(Zo=50): 1.4:1

Directivity:  16.95 dB

Max gain: 14.68 dBi (elevation 13 deg.)

Front-to-back ratio: 14.97 dB

Note: Obviously, this antenna is cut for the quite specific purpose of SSB weak signal work. with a design frequency of 50.130 mHz. Most weak signal SSB traffic is between 50.120 and 50.170, predominantly on or very near the SSB calling frequency of 50.125.


Key Physical Measurements:

Radiating Element Spreaders:  1.082 meters        Boom position:  0.00

Reflector Element Spreaders:   1.150 meters         Boom position: -1.050 meters

Director Element Spreaders:    1.050 meters         Boom position +1.500 meters

 

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Home Brew Projects

  1. Six Meter Quad

  2. Switchable L Tuner

  3. VHF/UHF Yagis

  4. Portable Power

  5. Portable Dipole system (Buddiipole)

  6. Heavy Duty Rotator

  7. Low-cost boom mike

  8. K3 “breakout box”

  9. All brass iambic key