G0KSC SC14409 9el 144Mhz Yagi Antenna with a 4.35 Metre Length Boom
This is a good wide band Yagi optimised for 144 to 144.600Mz. It has a mid-sized length boom of 4.35 metres and therefore can be made from a single piece 1.25 inch square tube section. No boom support will be required.
Remember, this is a very wide band Yagi although it only has 9 elements it provides good forward gain. Performance of this antenna is very good with maximised radiation efficiency and very low loss. Take a look at the images below.
Front to Back ratio has been tuned to allow you to still hear signals from behind although well down on the forward signal. This will ensure any rearward DX will be heard too!
Dimensions in Metres
Element spacing:
- Ref = 0
- Driven = .207
- D1 = .320
- D2 = .739
- D3 = 1.367
- D4 = 2.08
- D5 = 2.866
- D6 = 3.712
- D7 = 4.35
Element sizes per element half:
- Ref = .5095
- Driven = .5125
- D1 = .479
- D2 = .467
- D3 = .454
- D4 = .445
- D5 = .438
- D6 = .4375
- D7 = .4395
Performance figures @ 144.300Mhz:
- Froward Gain: 14.15dBi free space
- Front to Back: 22.07dB
- Radiation angle at 10 Metres above ground: 3 degrees
Element diameter:
Each element is made out of single piece 3/8 inch (9.525mm) 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 1.25 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 10mm 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.
Andy VK6OX built his antenna
Andy made an excellent job of the feedpoint too.
Andy made these comments about his antenna:
The subject yagi is now completed and essentially ready for operation. The included pics show the dipole feed assembly partially sealed (I wanted to make sure that the silicone sealant didn’t create any adverse effects to the matching before completely sealing). The balun will also be wrapped in Scotch 23 Self Amalgamating tape then covered with Scotch 33+. The white cable ties will be replaced with SS straps prior to final install.
The minimum SWR is at ~144.350MHz – 1.02:1, so as far as matching is concerned, this is good! SWR at 144.100MHz is 1.05:1 and also at 144.500MHz. This is a very good result! Element lengths and spacing are unchanged from original.
Andy VK6OX
