A Yagi Antenna for Amateur Satellite Operation

Posted on February 22, 2018

After a disappointing morning of making no contacts on HF, I decided that I wanted to try working some amateur radio satellites. After doing a little reading, I realized that the antenna I had already wasn’t going to cut it to work satellites, and I needed something with a bit of gain. I decided to roughly follow this guide, but I wanted a shorter antenna, so I substituted in different values for the elements.

Measurements

For the 70cm antenna, I went with a 5 element design, as it was about the length of the 2m 3 element yagi. I took the values from the K1FO example in W9CF’s yagi simulator, and are listed here:

70cm yagi dimensions

Element distance from start length(cm)
R 0cm 33.8cm
DP 10.4cm 33.2cm
D1 14.6cm 31.3cm
D2 22.4cm 30.4cm
D3 33.2cm 29.7cm

W9CF’s program gives this yagi a gain of 9.43dBi and a beam width of almost 90 degrees.

The 2m yagi was calculated using this calculator, for a frequency of 145MHz, and 3 elements.

2m yagi dimensions

Element distance from start length
R 0 99.7cm
DP 49.7cm 98.5cm
D1 65.2cm 94.1cm

The calculator above gave the antenna a gain of 5.23dBd or 7.38dBi of gain.

Materials

To build the antenna, I used the following:

Material Purpose Cost($)
5pc. 30.5cm Brass Rod 70cm elements 5
6ft poplar board Base for antenna 4.08
10ft, 10ga bare copper wire 2m elements 3.50
Total N/A 12.58

Construction

Mesurements

I first began by laying out the longer 2m yagi antenna, so leaving some space for holding the board, I marked out the positions of the director, dipole, and reflector. Then I began marking for the 70cm antenna, by measuring the reflector position so that the dipole of the 70cm antenna was at the same position as the 2m dipole. Finally, I marked the positions of the 3 reflectors for the 70cm antenna, and where to cut the wood to length.

70cm elements

The 70cm elements were formed out of 5, 12" lengths of 3/32" brass rod, and a 12" section of 1/8" diameter brass tube. The pieces were cut as follows:

Rod # Cut short piece long piece
1,2 16cm 14.5cm -> D3 16cm -> R
3,4 15cm 15 -> D2 15.5 -> D1
5 15.25cm DP DP

The rod pieces are slightly shorter than each element, so the remaining length comes from a spacer inside the brass tube which joins the two halves in the center. For each element (except dipole):

  1. A 1.5" piece of brass tube was cut and deburred

  2. The pieces were measured and a small spacer was inserted if needed.

  1. Flux was applied to the two rods and they were taken outside

  2. The center piece was heated with a torch, and solder was applied to each joint

  1. Finally a piece of coax was stripped, and the shield and core soldered to the two pieces of the dipole

Partially finished Product

2m yagi

The construction of this part was much simpler than the 70cm bit. Namely, I:

  1. Transferred the positions of the 2m elements to the other side of the board and cut grooves for the pieces to sit in.

  2. Cut the pieces of copper wire to length and cut the dipole piece in half

  3. Soldered a short stub of coax to the 70cm dipole and ran it around to the other side of the board

  1. Soldered the coax to the 2m dipole and taped everything in place