G0KSC SC14408L 8el 144Mhz Yagi Antenna with a 3.4 Metre Length Boom

This antenna has been redesigned and represents what i beleive to the the 'ideal boom length' for an OWA direct feed 50 Ohm Yagi with 8 elements on 144MHz. This can be seen in the model in the super flat SWR, the high levels of F/B ratio along with the excellent gain and very low-noise pattern.

The model below is designed with 12.7mm / 1/2 inch elements. If you require a version of this antenna with another diameter wire, Email me and I will remodel. It is NOT POSSIBLE to simply resize the elements when using a VERY different diameter wire and get the best performance possible, Spacing and element diameters MUST be re-optimised.

REMEMBER, Gain does not make the best antenna on 2m. F/B, SWR Banwdith, Pattern Stability, Side Lobe suppression, Sky Teperature and G/T all play a role. Choose an antenna and gain alone and you will never know what you are missing!!

SC14408L by M5TAW

Dimensions in Metres - all tubing 1/2 inch or 13mm diameter, mail for other sizes and tapered elements

Element spacing:

• Ref =      0
• Driven =  .360
• D1 =       .495
• D2 =       .877
• D3 =      1.419
• D4 =      1.993
• D5 =      2.683
• D6 =      3.418

Element sizes per element half:

• Ref =       .5055
• Driven =   .504
• D1 =         .471
• D2 =         .456
• D3 =         .440
• D4 =         .4325
• D5 =         .422
• D6 =         .3975

Performance figures @ 144.300Mhz:

• Froward Gain: 12.80dBi free space
• Front to Back: 26.83dB

Sky Temperature @ 144.100MHz = 247.5 Kelvin

G/T @ 144.100MHz = -11.17dB

Dimensions in Metres - all tubing 12mm diameter, mail for other sizes and tapered elements

Element spacing:

• Ref =      0
• Driven =  .360
• D1 =       .495
• D2 =       .877
• D3 =      1.419
• D4 =      1.993
• D5 =      2.683
• D6 =      3.418

Element sizes per element half:

• Ref =       .5065
• Driven =   .504
• D1 =         .472
• D2 =         .457
• D3 =         .441
• D4 =         .4335
• D5 =         .423
• D6 =         .3985

Performance figures @ 144.300Mhz:

• Froward Gain: 12.78dBi free space
• Front to Back: 26.76dB

Azimuth Plot

Elevation Plot

This fantastic antenna at 10m up

An Excellent SWR to go with the fantastic pattern!

Remeber, mail me if you have different diameter tube requirements and send photos of built antenna!

G0KSC SC6-4-6D 6el 50Mhz/70Mhz Dual Band Yagi Antenna with a 3.2 Metre Length Boom

About this Antenna

This is what is known as an 'interlaced' Yagi as both a 50Mhz beam and a 70Mhz beam (there are no common elements) are interlaced and sitting on the same boom. This presents a huge advantage over beams which use common elements with traps a coils. Firstly, these traps and coils present a loss within the antennas elements. In addition, the spacing of elements is a compromise to make a 'best job' for both bands.

None of the 70Mhz elements are physically connected to the feed point. The 70Mhz antenna is feed by it's closeness to the 50Mhz elements. i.e. the driven element of the 70Mhz Yagi sitting closely to the 50Mhz driven. It is a little more technical than that but so as the masses can understand how it works. The antenna works as a 3 element beam on each band.

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 50Mhz and 70Mhz antenna elements are easily seen apart. These images are produced with EZNEC+. The red circle indicates the point of feed for the coax connection. one feed for both bands.

The SC6-4-6D Built and installed by PA0VAJ

Sizing and spacing are as follows:

Dimensionsin Metres

Element spacing:

• Ref 6     =     0
• Ref 4     =    1.325
• Driven 6 =    1.908
• Driven 4 =    2.028
• D1-6     =     3.135
• D1-4     =    3.186

Element sizes per element half:

• Ref 6     =       1.454
• Ref 4     =       1.041
• Driven 6 =       1.408
• Driven 4 =       1.001
• D1-6      =       1.293
• D1-4      =      1.01

Performance figures @ 50.250Mhz:

• Froward Gain: 8.05dBi free space
• Front to Back: 12.03dB
• Radiation angle at 10 Metres above ground: 15 degrees

Performance figures @ 70.250Mhz:

• Froward Gain: 8.44dBi free space
• Front to Back: 12.43dB
• 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.

Below are two images showing current distribution through the antenna on both 50Mhz and 70Mhz. This current is represented by the line lines overlaying the elements. The higher the line is away from the element, the higher the current. Following these are performance images including plots and SWR sweeps.