G0KSC SC0405L 5el 70Mhz Yagi Antenna with a 3.15 Metre Length Boom

This is my 'Long Boom' 5el Yagi for 70 Mhz. It has a boom length which is made from a single piece 1inch square tube section. No boom support will be required.

I designed this antenna to give a little extra than usual forward gain at the sacrifice of a ultra flat SWR curve and some front to back ratio. This is due to the fact 70Mhz is a quite band so front to back should not be so important.

The SC0405L built by M0WBM

Standard G0KSC insulators can be used with this model to good effect. Antenna sizing as follows:

Dimensions in Metres

Element spacing:

• Ref =      0
• Driven =  .408
• D1 =      .768
• D2 =     1.914
• D3 =     3.146

Element sizes per element half:

• Ref =       1.053
• Driven =   1.026
• D1 =       .977
• D2 =       .953
• D3 =       .933

Performance figures @ 70.200Mhz:

• Froward Gain: 10.94dBi free space
• Front to Back: 18.01dB
• Radiation angle at 10 Metres above ground: 10 degrees

Element diameter:

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.

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.