G0KSC SC0407L 7el 70Mhz Long Boom OWA Yagi Antenna with a 6.63 Metre Length Boom
This is a nice DX bean for 70 Mhz. 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 1.25inch box section with a 2 metre piece of 1inch box section slotted into and bolted to the director end of the boom to make up the additional 1.63 metres. The mounting point should still be in the centre of the 5 metre 1.25 inch section as the higher concentration of elements at the reflector end will counter balance the extended end of the antenna.
Dimensions in Metres
Element spacing:
- Ref = 0
- Driven = .716
- D1 = 1.082
- D2 = 2.144
- D3 = 3.655
- D4 = 5.153
- D5 = 6.63
Element sizes per element half:
- Ref = 1.049
- Driven = 1.022
- D1 = .974
- D2 = .942
- D3 = .93
- D4 = .917
- D5 = .837
Performance figures @ 70.250Mhz:
- Froward Gain: 12.62dBi free space
- Front to Back: 26.82dB
- Radiation angle at 10 Metres above ground: 10 degrees
Element diameter:
Each element is made out of single piece 1/2 inch (12.7mm) aluminium 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.
NOTE:
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.
