Construction Details

2-El.-12,5-Ohm (0,40 m)   

2-El.-28-Ohm (0,60 m)

3-El.-12,5-Ohm (1,90+2,20 m) new

3-El.-28-Ohm (1,90 m)

3-El.-28-Ohm (2,50 m)

4-El-12,5-Ohm (2,90 m)

4-El-12,5-Ohm (3,60 m)

5-El.-28-Ohm (4,50 m)

5-El-12,5-Ohm (6,00 m)

5-El-18-Ohm (6,00 m)

6-El.-28-Ohm (7,20 m)

7-El.-28+50Ohm (9,20+7,75 m) 8-El.-28-Ohm (12,30 m) 9-El.-28-Ohm (14,00 m)
4-El-28+50-Ohm (2,20 m) 5-El-50-Ohm (4,30 m) new 6-El-50-Ohm (6m+7,20 m) ne

2-Element-12,5-Ohm- Yagi with 0,40m-Boom

Complete description of all details for building this Yagi and stacking to an array




Short data: Gain 4.7 dBd, F/R >20dB

Bandwidth 300 KHz (50.0-50.3 MHz) at SWR < 1.5, -3 dB hor. 66,6°, -3 dB vert. 123,4°

The antenna has an unbelievable pattern, but must have a very clear surrounding! Do not use this Yagi in a "christmas-tree" of other antennas.

The UKSMG-Contest 2009 was won with the stacked array 2 over 2 as you see in the picture right.

Stacked Array: Gain > 8 dBd

A 2-Element-Yagi for 50MHz (Report in the UKSMG "Six News", Issue 96, Aug. 2008)

The 2-element-Yagi is the most effective directional antenna. One additional element parasitic coupled with a length of about a half-wave to a dipole will increase the gain from 0dBd to 4-5 dBd. Further 4,5 dB more gain would need a 5- to 6-element Yagi with a boom-length of 1 λ! The ARRL-Antenna-Book says about the 2-Element-Yagi “The most bang for the buck”. 

A two-element Yagi with a director needs a spacing of 0,05-0,1 λ, the feedpoint impedance drops down to 10-25 Ω. This makes it possible to feed a 12,5-Ω-Yagi with the very simple “DK7ZB-match”, which was introduced first in 1995 [1]. This match uses two 50-Ω-cables with an electrical length of λ/4 in parallel as a quarterwave-impedance-transformer with a Z=25 Ω. The principle of the DK7ZB-match is shown down. 

The two cables are wound to a coax-choke and give a very good suppression of screen-waves. In the meantime a lot of yagis built by hams all over the world use this simple match with good success. For an impedance of 28 Ω the same method can be realized with two parallel λ/4-75-Ω-cables

The dimension of the yagi was designed with EZNEC+5 [2] for a resistitive load of 12,5 Ω and an element distance of 40 cm (0,067 λ).This gives a gain of 4,7 dBd, a F/B ratio of 17 dB and a bandwidth of 300 KHz for a SWR <1,5.  The free space patterns (azimuth and elevation) are shown in the pictures down, the SWR-graph see above.  


You must use the exact given dimensions, the tapering and the diameters are very critical. Other tube diameters need a new calculation!

 Table 1: Lengths and dimensions of the Yagi

  Position Length 10/8 mm Length 12 mm Length 7/16''+3/8''
Radiator 0 mm 2976 mm 2950 mm 2968 mm
Director 400 mm 2842 mm 2816 mm 2830 mm

Building up the beam

For lightweight portable operation I use a middle part of 2x25 cm with aluminium tubes 10x1 mm, the outer element parts consist of 8x1mm tubes. For a more stable construction at home it is better to use 12x1 mm aluminium (table 1) for the full length. The given length of the radiator is from tip to tip with an insulated part of 12 mm in the middle of the element (pictures at the end of the site). For the non metric tubes I give dimensions in inch in the table above.


The boom is made of 20x20x1,5 mm square aluminium, for the mounting of the director I use TV-clamps (polyamid). See the picture above for the details.   

The impedance choke is made of two pieces of RG174 in parallel, each length is exactly 1 m long, which refers to the screen and is λ/4*V long (V=0,667).  The construction (picture 5) will handle 200 Wtts SSB/CW, if you will use higher power up to 500 Wtts you must take the same length of RG-58. In that case the choke must be mounted outside the box. The coax socket is grounded to the boom, this gives a better sleeve-wave suppression than the choke alone.  

Getting in the air

The antenna with its small bandwidth is very sensitive to the surrounding, a clear neighbourhood will be needed for a perfect working. The minimum distance to earth is 3m, in that height you can test the antenna. The resonant frequency can be changed by making the radiator longer or shorter. If the impedance is to high, the director must be made longer, if it is to low, you must shorten it a bit. The best SWR should be reached at 50.150MHz.

Stacking the Yagis

The stacking cable is made of 2x3/4-λ coax-cable with 75 Ω, this will give an additional SWR <1,15. The ideal resistance for the impedance would be 71Ω, but such cable is not available. I use RG-59B/U in MIL-quality, with a length of exactly 2x3m. For higher power each 75Ω-cable is suitable (e.g. RG-11), but you must know the right V (velocity of propagation) for the correct 2x3/4-λ pieces. It is recommended to test the stacking cable with two 50Ω-dummies for correct function.


The vertical  pattern for free space is shown above. For the case that the heights of the two antennas are 6 m and 10 m above a ground with medium conductance I have simulated the vertical pattern in the picture below. This configuration I have used in the 2009 UKSMG-Summer-Contest with big results!

Meanwhile a lot of 50 MHz-Stations in all continents use DK7ZB-designed homebrew antennas. The principle is easy matching and good performance. If you are interested in more 50 MHz-Yagis, please look for the other antennas on my page.

Photos and comments for my website are very much appreciated.


[1]  Steyer, M. (DK7ZB): Einfache Speisung von Monoband-Yagis, FUNKAMATEUR (44) 4/95, S.406

[2] Program EZNEC+5 by Roy Lewallen, W7EL,

[3] Homepage DK7ZB,   

Mounting of the Director (12 mm) with an insulated clamp and 20x20 mm-Boom