Intro: Antenna Balun for a Folded Diapole
Every body sometime or the other will come to a point of installing an antenna, and here i would like readers to shed light on the Baluns that will be very useful for feeding a Folded Diapole as shown in the figure.
A Folded diapole antenna has a central impedance of 300 Ohms and thus, you will need a ladder line or a straight cable to take the feed to the receiver or a transmitter. But now a days ladder line are not much used and you will find a lot of coax cables in the market that are found cheap. But to make direct connections to the antenna will not be a proper way as the coax cables have impedance of 75 Ohms, therefore to make a diapole from unbalanced to balance you need to make a balun and i will be showing you here how that would be done in an easy manner.
This is a 4:1 balun that i will be showing to you all.
Step 1: Selecting the Exact Frequency You Want
Here you need to perform a simple calculation on what is the frequency you would like to receive with the antenna. In my case i had prepared the antenna for a FM DX antenna, meaning i wanted to receive more distant FM radio stations in my receiver.
The FM radio frequency spectrum starts from 88 MHz to 108 MHz, therefore taking the mid frequency of 97 MHz you would be able to receive all the frequency from 88 MHz to 108 MHz.
But in this instructable i am talking about the preparation of Balun keeping in mind that you have you antenna complete. But if you still don't know the basic of antenna making, go to the web site that i have provided in the link
In this website you will find all the details.
Step 2: Installation of the Dipole
As i have given a rough idea about the installation of the diapole, kindly go through the images.
Step 3: Making the Dipole Connections
You can make the connections as shown in the figure. You can find the length of the co-axle cable to be wound from the previous website that i had given, in my case it was for an FM antenna and i needed to cut a length of 1.3m of Co-Axle cable to be wound as a phasing section.
The website for calculating is
Step 4: Installation
Here the correct way to install the 1.5m length of co-axale cable is shown as such. it should be wounded and then connect to the respective connector
I used a cable TV connectors which are available very cheap.
After installation i had checked with my DBV-T SDR dongle and i could receive many DX Nepal and Bhutan FM stations and it is working flawlessly.