G0KSC SC0404S 4el 70Mhz Yagi Antenna with a 1.457 Metre Length Boom

This is my smallest 70 Mhz beam. It has a short length boom which is made from a single piece 1inch square tube section. No boom support will be required.

This antenna shows good performance particularly when stacked. Take a look at the last plot on this page which shows the pattern 7 metres above ground with 2 beams, one stack 2.1 metres above the other.

Dimensions in Metres

Element spacing:

  • Ref =      0
  • Driven =  .409
  • D1 =      .600
  • D2 =     1.457

Element sizes per element half:

  • Ref =       1.053
  • Driven =   1.015
  • D1 =       .981
  • D2 =      .943

Performance figures @ 70.200Mhz:

  • Froward Gain: 8.84dBi free space
  • Front to Back: 17.33dB
  • Radiation angle at 10 Metres above ground: 10 degrees (5 degress for 2 stack)

 

Element diameter:

Each element is made out of single piece 1/2 inch (12.7mm) aluminium 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.