G0KSC SC2807M 7el 28Mhz Yagi Antenna with a 13.6 Metre Length Boom
This antenna has been designed for someone who loves 28mhz and who has a bit of space too! Working the WHOLE BAND from 28Mhz to 29Mhz, not just the CW or SSB portion. With great gain and front to back ratio to boot. Power limitations are whatever the limit of your coax is so if you have good coax, 3KW+ is not a problem.
This Yagi has been designed to be built on a boom of 3 sections. The centre section should be a 5 metre length of 2 inch aluminum tubing whilst the out 2 sections should be 1, 3/4 inch tubing slotted in to the 2 inch section by around 600mm each end. Boom guying to the main mast will be required.
If G0KSC insulators are to be used, these should be engineered to be 300mm long rather than 100mm and the width of each also should be doubled.
Small errors in your measurements or calculations when building this antenna WILL NOT greatly affect performance due to it's non-critical design.
Dimensions in Metres
- Ref = 0
- Driven = 1.719
- D1 = 2.468
- D2 = 4.668
- D3 = 7.899
- D4 = 10.996
- D5 = 14.089
Element sizes per element half:
- Ref = 2.619
- Driven = 2.564
- D1 = 2.444
- D2 = 2.397
- D3 = 2.367
- D4 = 2.364
- d5 = 2.256
Performance figures @ 28.500Mhz:
- Forward Gain: 12.35dBi free space
- Front to Back: 22.1dB
- Radiation angle at 10 Metres above ground: 15 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 2inch or 3 inch boom as the elements sit high enough above the boom for the boom to have no influence.
If you are only able to obtain 1/2 inch elements in 6 metre lengths and can only obtain 5 metre lengths, join them in the middle at the insulator with a small piece of 3/8 inch tubing (600mm long) bolt the element to the insulator with 2 bolts either side of the boom.
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.