Antennas – eaktronix http://eaktronix.com Sun, 17 Jan 2021 21:43:17 +0000 en-US hourly 1 https://wordpress.org/?v=6.9 http://eaktronix.com/wp-content/uploads/2026/01/cropped-logo2-32x32.jpg Antennas – eaktronix http://eaktronix.com 32 32 Portable antenna at 5 euros for the 2 meter band (144-146 MHz) http://eaktronix.com/portable-antenna-at-5-euros-for-the-2-meter-band-144-146-mhz/ Sun, 17 Jan 2021 11:04:33 +0000 http://eaktronix.com/?p=574 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).

  • fig.1
  • 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.

  • fig.3
  • fig.4

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.

  • fig.5
  • fig.6
  • fig.7

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.

  • fig.8
  • fig.9
  • fig.10

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.

  • fig.11
  • fig.12
  • fig.13
]]> Baofeng UV5R Comparison of the original antenna with a counterfeit on the NA-771 http://eaktronix.com/baofeng-uv5r-comparison-of-the-original-antenna-with-a-counterfeit-on-the-na-771/ Sun, 17 Jan 2021 10:51:34 +0000 http://eaktronix.com/?p=571
fig.1

tags: Baofeng UV-5R, NA-771 Nagoya, comparison

Here I am comparing the SWR of the original antenna with that of the obviously counterfeit Nagoya NA-771 antenna.
As can be seen in fig.2 which concerns the original antenna, the latter has a good adaptation in the 2 meter band. In the 70 cm band it is out because its resonance arrives rather than expected, ie at 405 MHz. Around 450 MHz, the antenna is suitable for a ROS 3, which is not perfect, but usable. In fig.3, on the other hand, there is an antenna that cannot be used in the bands provided. In the band around 144 MHz, it has an S11 of -2 dB, and at 70 cm, it has an S11 of -1 dB. Despite the fact that the antenna costs only 3 euros on Amazon, it is still not good to sell antennas that do not work. In practice this manifests itself in permanent cuts with the UHF relay, things that do not happen with the original antenna in my case.

  • fig 2.original
  • fig 3.fake of the NA-771

]]> Yagi antenna for the 70 cm band (430-440 MHz) http://eaktronix.com/yagi-antenna-for-the-70-cm-band-430-440-mhz/ Sat, 09 Jan 2021 21:15:36 +0000 http://eaktronix.com/?p=562

tags: yagi antenna, 70 cm, cheap, simple
This Yagi antenna that I present here was developed with the aim of capturing signals between 430 and 440 MHz from amateur radio satellites. The antenna has three elements and is relatively simple to make and very low impact.
The simulation of the digital model made it possible to fix the dimensions of the antenna and to obtain a prognosis on the bandwidth. In Figure 1 we note that the passband at -10 dB (SWR 2: 1) ranges from 427 to 458 MHz.

Fig. 1, S11 simulated

The antenna support is a square PVC profile with side 11.5 mm.
The gap between the reflector and the director is 300 mm. The director and the reflector are made with a threaded rod of diameter 4 mm.

  • Fig. 2, Square PVC profile
  • Fig. 3, Reflector (bottom) and director (top) of the antenna


The driver element is a folded dipole made from RG316 coaxial cable.
The total length of the dipole is 300 mm. In order to give rigidity to the cable, the latter is inserted into a PVC tube in which an opening is created in order to weld the attack line.

  • Fig. 4, Structure of the dipole
  • Fig. 5, Dipole assembly


The antenna is almost finished,
just insert the threaded rods and glue the dipole with a glue gun. The ends of the PVC tube are also filled with glue.

  • Fig. 5, Gaps between elements
  • Fig. 6, Dipole bonding
  • Fig. 7, Glue in the PVC tube
  • Fig. 8, Antenna completed


The measurement of the SWR of the manufactured antenna (fig.
9) shows that the antenna has a bandwidth between 419.5 and 451.2 MHz for a SWR of 2: 1.

Fig. 9, S11 and measured ROS of the antenna


In terms of antenna gain, the simulator promises a gain of around 7.8 dBi.

Fig. 10, Antenna gain simulated
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