3D printed parts for 7 element I0QM 144 MHz band Yagi

7 element yagi

homemade partly 3D printed IQ0M 7 element 144 MHz Yagi below a commercial 23 element 1296 MHz Yagi

The link below takes you to a PDF describing I0QM's seven element yagi for 144 MHz:
I0QM 7 element Yagi

I0QM designed the antenna to have a 50 ohm feed impedance at the center of the driven element, so in principle you can directly attach 50 ohm coax. The author suggests using a 1:1 balun (e.g. a bazooka balun). I wont mention any more about the design here as you can get all the details on the link.

I first made a version of this antenna in 2016 and found it had a very good forward gain and good gain bandwidth and 'SWR bandwidth' over the SSB part of the 2m band. It seemed to be almost perfect ... however although it worked great when dry the SWR went high when the antenna became wet after rain.

My prototype used a wooden boom but you will notice that I0QM does not mention anything about the boom material. I have used wooden booms for 2m band antennas in the past with great success (they are cheap, light weight and easy to maintain) so it was dissapointing that I had this problem on what looked like a good design.

element boom fixing

Metal boom 3D printed version
I had a 4m 19 mm diameter aluminium tube taking up valuable space in my workshop and so I decided to cut it down a little to make the metal boom for this version of the I0QM antenna. I also used 6 mm diameter rod elements instead of the 4 mm aluminium welding rods used for the MK I wooden version. I decided that I would design my own 3D printed element and driven element fixings (see photos). Unsurprsingly this antenna also worked very well. I was able to have both antennas up at the same time and showed they gave identical results, but I still found the SWR changed when it got wet!

7 element yagi feed point

Metal boom version with rain hood
You can see from the pictures that the two dipole halves of the driven element used four bolts to secure them at the center. Two longer bolts are used closest to the center to connect to the 1:1 balun and coax. They were long enough that I decided to use them to support a 3D printed rain hood to protect the area around the fed point. So far this seems to have solved the SWR-rain issue.

3D parts layed out

3D printed parts
The pictures show i) the 3D printed parts spread out before assembling, ii) one of the directors attached to a fixing along the boom, iii) the feed point showing four bolts securing the two sides of the dipole, iv) the same with the hood to protect the feed area from rain and v) the complete antenna on the mast (with a 23 element 23 cm antenna above it).

I tried two versions of the dipole center holder. The one used here has an insulating cyclinder, between the two dipole halfs, to try and make sure that any water that falls on this part of the antenna flows away (rather than stay in the cyclindrical gully formed to take the two rods).

A few comments:
I made my 3D parts for a 18-19 mm diameter aluminum tube / boom as I just happend to have this available. Other boom diameters or a square boom for example could of course be used and the 3D printed parts modified accordingly.

I0QM 7 element Yagi boom fixing:
".stl" file
".scad" file
".g" file
feed point fixing:
".stl" file
".scad" file
".g" file
rain hood:
".stl" file
".scad" file
".g" file
back to
3D page


Dr Jonathan Hare University of Sussex, Brighton.
e-mail: j.p.hare@sussex.ac.uk

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