Introduction: Yagi UHF Antenna for the 70 Cm Band (430-440 MHz) by F4HWK
In this tutorial i show you how to build a Yagi antenna for the 70 cm band (430-440 MHz). This antenna can be used to receive the ham satellite communications with any portable UHF receiver.
Here i provide all build steps, with all dimensions you need. At the end as usual i provide SWR measurements to confirm its performances in terms of impedance matching.
You can also find some simulation results on my blog as well as the estimated gain: http://kavea.free.fr
Step 1: Reflector and Director Elements
Reflector and director of this three element Yagi are made from 4 mm diameter threaded rods. The length of the reflector is 345 mm and the length of the director is 276 mm. These elements are mounted on a square PVC bar 11.5 x 11.5 mm with butterfly screws. The distance between the reflector and the director is 300 mm. Cf. photos.
Step 2: Driven Element
The driven element of this Yagi is a folded dipole which i made from a piece of RG316 cable. The total length of the dipole is 30 cm. In order to transform this piece of coaxial line into antenna you need to remove a bread shield in the middle of the coax, and solder braid shield to a central conductor at its both ends (cf. photo). To give some rigidity to the dipole you need to insert it into a PVC tube with a cut out window. So that you can solder a feed line to the dipole (cf. photo).
Step 3: Assembling
The final step is to assemble all parts together. Insert the reflector and the director into a PVC bar holes, then with a hot glue attach the driven element to the PVC bar, 150 mm away from two others elements. Put some hot glue inside the PVC tube holes to ensure the impermeability of the antenna.
Step 4: Measurements
The developed antenna has been measured with a VNA in terms of SWR and S11 parameters. The result shows that antenna has a bandwidth between 419.5 and 451.2 MHz with the respect of SWR of 2:1, which is more than enough for the 70 cm band (430-440 MHz).