tags: VHF portable antenna, DIY antenna, cheap antenna
Here I present a portable Yagi type antenna for the 2 m band, i.e. 144-146 MHz. This is very easy to do, deploys in less than 1 minute and costs only 5 euros.
The design of this antenna was made from an electromagnetic simulation of FEM type. The parameters have been optimized in order to obtain maximum gain starting from a design of a Yagi antenna with two elements, which are the excitation dipole and the reflector. The material necessary for the manufacture of the antenna is illustrated in FIG. 1, it is easily found on the market, but for this antenna everything was purchased from leroymerlin, the store references are given. The material is composed of 3 threaded rods with a diameter of 4 mm (ref. 65299675, 0.52 euro / piece), a square PVC tube with a 15 mm x 15 cm section and a length of 1 m (ref. 65289994, price 2.8 euros ) and some nuts and bolts. You will also need something to cut / saw the rods and a drill (fig. 2).
The dimensions are given in mm in figure 3. From bottom to top we have the strand of the reflector made up of two parts, the total length of which is 98 cm. Then the two identical strands of the dipole. And finally the support, which is the PVC tube with the drilled holes. To power the dipole you also need a piece of coaxial cable. For my part I used an RG316 type cable. The important dimension concerning the latter and the length of the hooks which must be within 40 mm.
The final antenna as well as some technical details on the assembly are given in figures 5,6 and 7. It is noted in figure 6 that an adjustment of the SWR is possible by unscrewing the locknut and varying the length of overtaking.
After assembly and adjustment of the SWR according to figure 6, it should look like what I measured in figures 8,9 and 10. Namely a very good match between 144 MHz and 146 MHz (SWR of 1.2 ). At SWR of 2 the bandwidth is relatively wide and ranges from 138 MHz to 151 MHz.
Finally in terms of gain, the 3D simulation of the antenna promises us a gain of around 6.2 dBi (fig. 11-13), which is pretty good for a 2-element Yagi antenna.