G0KSC SC2805M 5el 28Mhz Yagi Antenna with a 5.6 Metre Length Boom
This is a good wide band Yagi for 28 to 29Mhz with a real flat SWR curve and good F/B. It has a short length boom of 5.6 metres and therefore needs to be made with a 2 piece boom of either 1, 1/2 inch, 1,3/4 inch or 2 inch square. No boom support should be required with 2 inch but it is likely sag will occur with the other sizes and therefore, boom guying to the main mast will be required.
Small errors in your measurements or calculations when building this antenna WILL NOT greatly affect performance due to it's non-critical design.
The 5el SC2805M at VK2ZT
Dimensions in Metres
- Ref = 0
- Driven = 1.093
- D1 = 1.407
- D2 = 3.07
- D3 = 5.606
Element sizes per element half:
- Ref = 2.666
- Driven = 2.605
- D1 = 2.47
- D2 = 2.428
- D3 = 2.299
Performance figures @ 28.500Mhz:
- Froward Gain: 9.49dBi free space
- Front to Back: 22.52dB
- 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.