G0KSC SC0409L 9el 70Mhz OWA Yagi Antenna with a 8.66 Metre Length Boom
This is a nice DX bean for 70Mhz. As always it has a nice flat SWR curve and is built with in a non-critical format so any small errors you make whilst constructing will not have a huge impact on performance.
I recommend this to be built from a 5 metre length of 1.25 inch box section aluminum with a 1 inch 5 metre length cut in to and slotted into each end.This should not need any support
Dimensions in Metres
- Ref = 0
- Driven = .79
- D1 = 1.17
- D2 = 2.197
- D3 = 3.638
- D4 = 5.276
- D5 = 6.5
- D6 = 7.513
- D7 = 8.655
Element sizes per element half:
- Ref = 1.043
- Driven = 1.028
- D1 = .980
- D2 = .954
- D3 = .934
- D4 = .915
- D5 = .885
- D6 = .901
- D7 = .915
Performance figures @ 70.250Mhz:
- Froward Gain: 13.98dBi free space
- Front to Back: 32.15dB
- Radiation angle at 10 Metres above ground: 10 degrees
Each element is made out of single piece 1/2 inch (12.7mm) aluminum tubing Each element half length needs to be doubled in order to gain your total element size. No difference is length needs to be calculated for the 1inch or 1,1/4 inch boom as the elements sit high enough above the boom for the boom to have no influence.
You can build this antenna with 13mm diameter tubing using the same parameters above. Slightly higher front to back ratio and forward gain will be seen along with a narrower SWR curve.
For construction information see 'G0KSC insulators' and the UKSMG article from the main menu on the home page.