G0KSC SC28-6-9D 11el 28Mhz/50Mhz Dual Band Yagi Antenna with a 4.76 Metre Length Boom

About this Antenna

I am particularly pleased with this design as I have not seen anything similar around on the Internet today yet with many HF radios including  six metres and occupying the same SO239 socket on the back of the rig, a good beam for ten and six was a must!

This is what is known as an 'interlaced' Yagi as both a 28Mhz beam and a 50Mhz beam (there are no common elements) are interlaced and sitting on the same boom.

The next interesting feature is the fact none of the 50Mhz elements are physically connected to the feed point. The 50Mhz antenna is feed by it's closeness to the 28Mhz elements. i.e. the driven element of the 50Mhz Yagi sitting closely to the 28Mhz driven. It is a little more technical than that but so as the masses can understand how it works. This antenna performs as a 4 element beam on ten metres and a 5 element beam on six metres.

The Interlaced OWA design removes these restrictions from the mix. With no losses from matching and just one feed point you have a winning formula!

Design Considerations

Interlaced, single feed point Yagi's are hard to model and there is some interaction between the elements. As a result, I have had to compromise a little more than one normally would have to in order to achieve my performance directives. In this case, I have sacrificed a little Front to Back ratio in an attempt to maintain as flat an SWR curve as possible. There are a couple of reasons for doing this. One, of course is to give as much bandwidth as possible but mainly, as with all antennas on this site, if the SWR curve is wide and low, any small mistakes in sizing and spacing by the builder will not make a tremendous impact on the antennas overall performance.

The image below shows how the antenna looks. The 28Mhz and 50Mhz antenna elements are easily seen apart. These images are produced with EZNEC+ whilst the balance of images below are produced within 4nec2.

Installed and built by PY1XZ

The G0KSC 28/50 dualbander at DH8BQA

The SC28-6-9d RevB built by G0KSC/G8FJG installed at G8FJG

Current distribution for each band is highlighted (pink lines) within the 2 images below. The further away the pink lines are from the element, the higher the current at that point within the element. The first image is for 28Mhz and the second image represents 50Mhz.

Sizing and spacing are as follows:

Dimensionsin Metres

Element spacing:

• Ref 28     =     0
• Ref 6     =     .579
• Driven 28 =    1.553
• Driven 6 =     1.466
• D1-28     =     2.477
• D1-6     =      1.94
• D2-28     =    4.864
• D2-6     =      2.915
• D3-6     =     4.76

Element sizes per element half:

• Ref 28     =      2.614
• Ref 6     =        1.469
• Driven 28 =       2.538
• Driven 6 =        1.438
• D1-28      =      2.39
• D1-6      =       1.401
• D2-28      =      2.258
• D2-6      =       1.37
• D3-6      =      1.405

Performance figures @ 28.500Mhz:

• Froward Gain: 8.72dBi free space
• Front to Back: 16.33dB
• Radiation angle at 10 Metres above ground: 15 degrees

Performance figures @ 50.250Mhz:

• Froward Gain: 9.47dBi free space
• Front to Back: 21.16dB
• Radiation angle at 10 Metres above ground: 15 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.

More performance images below: