G0KSC SC2803Q 3el 28Mhz OWA Quad Antenna with a 4 Metre Length Boom
This antenna produces 9.34dBi ofr forward gain with 32dB front to back ratio at 28.500 Mhz. This has been achieved over a respectable 500 Khz bandwidth on a boom of only 4 metres in length. This is around one metre+ less than would be required to see similar gain from a Yagi. In addition, I have been able to model the antenna without the narrow bandwidth characteristics normally associated with an antenna of this kind.
Bandwidth is a little smaller than on 50 and 70 Mhz as we are still using 2MM wire. If this was increased (which would need re-modelling) the bandwidth would be greater.
As with all my antennas, this is a non-critical design and therefore, any small errors in you calculations when building the antenna WILL NOT have a great impact on the antennas final performance.
Dimensions in Metres
- Ref = 0
- Driven = 1.8
- D1 = 4
Elements lengths - full quad length:
- Ref = 11.128
- Driven = 10.752
- D1 = 10.328
Performance figures @ 28.500Mhz:
- Froward Gain: 9.34dBi free space
- Front to Back: 32.13dB
- Radiation angle at 10 Metres above ground: 15 degrees
This antenna has been models with 12#/ 2.05MM copper wire. You will need to mail me if you wish to use a different gauge as the model will change. Isolated spacers will be needed. fiberglass would be a good option.
Build orientation is as per the layout image below with the feed point on the bottom section of the quad indicated by a red circle.
Feeding the Antenna
Whilst OWA is not normally a term used in quad antennas, I felt it appropriate due to the low SWR and wide bandwidth of this antenna. Like all of my antennas, this has a 50Ohm impedance so can be fed directly with 50Ohm coax, no matching is required. However, a balun or RF chokes should be used in the coax as close to the feedpoint as possible.