Introduction: DIY 5$ Portable VHF Yagi Antenna for the 2 Meter Band (144-146 MHz) by F4HWK
In this publication i explain how to build a very light weight, cheap, easy to build and deployable in 30 seconds portable VHF antenna for the 2 meter band. Here i present all steps to build this antenna. Measurement results for the S11 (or SWR) are also provided. The estimation of the gain for this antenna by an electromagnetic simulator is given on my blog :http://kavea.free.fr
Step 1: Materials and Tools
All you need for this antenna are 3 pcs of 4 mm diameter threaded rods, a PVC bar with a rectangular cross section (15 x 15 x 100 mm) and some screws. You also will need something to cut the rods and a drill.
Step 2: Dimensions
All dimensions are given in mm on the first figure. The antenna is a Yagi type antenna, so it is composed of one reflector, visible on the bottom part of the figure. The reflector is split in two parts, but its overall length is 98 cm. The main dipole on the middle of the photo has also two (hopefully) identical parts. Finally, on the top we can see the drilled PVC bar.
In order to connect the dipole you will need some coax cable. In my case it is an RG316. The feeding length of 40 mm visible on the second photo should be respected.
Step 3: Assembling
The assembled antenna should look like on photos.
Step 4: Tunning
If you have an antenna analyzer you can tune the antenna by increasing or decreasing the length visible on the photo. Otherwise, it should work fine if you have respected all dimensions.
Step 5: Measurements
Here i present the measured SWR of the antenna. As you can see, the impedance of the antenna is very well matched to a 50 ohm system. Between 144 MHz and 146 MHz, antenna has an SWR less than 1.2 . For an SWR of 2, the antenna has a bandwidth from 138 MHz to 151 MHz which is a pretty good result.