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G0KSC SC14405S 5el 144Mhz Yagi Antenna with a 1.391 Metre Length Boom
This is a good wide band Yagi covering the whole of the 2 metre band with an SWR figure less than 1.1 and at the same time exhibits a very good Front to Back ratio. It has a short length boom of 1.391 mtrs and therefore can be made from a single piece 1inch square tube section. No boom support will be required.
Remember, this is a short, very wide band Yagi so there is a little less gain than you could achieve from a beam with five elements. However, this antenna can be used to access your local repeater in vertical polarsation or for a bit of E's in the summer down on 144. Even sticking the back of the van and finding a nice hill somewhere is possible with this one too. With exceptional Front to Back ratio you will be in a position to null out strong local noise (such as local repeaters etc) in order to work stuff a little further a field.
The last photo in the list below shows the performance of 2 of these antennas with one stacked 1 metre above the other.
Dimensions in Metres
- Ref = 0
- Driven = .25
- D1 = .366
- D2 = .866
- D3 = 1.391
Element sizes per element half:
- Ref = .524
- Driven = .516
- D1 = .468
- D2 = .451
- D3 = .435
Performance figures @ 144.000Mhz:
- Froward Gain: 10.06dBi free space (this is the lowest point of gain, it gets higher up to 146Mhz)
- Front to Back: 28.71dB
- Radiation angle at 10 Metres above ground: 5 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.