What you do now is remove the shielding at the 1198mm mark for the 1498mm long coax cable. One which is the total length of the smaller loop (2276mm), one which is half the length of the larger loop (1198mm), and one which is a little longer than half the length of the larger loop (1498mm). Both ends of this cable are left OPEN! You should now have three pieces of coax.
The other length equal to half of the total length PLUS whatever you want as a connector for the antenna (1198mm + e.g. One length is equal to half of the total length given in the above calculator (2395 / 2 = 1198mm), and it also has core and shield solder together on both ends. Basically you just want a single length of conductor for the smaller loop. Now, the smaller inner loop is made of one length of coaxial cable, in which you solder the center lead and shield together at both ends. When actually constructing the antenna, make sure to use a little extra coax, so you can tune it later. Punch this into the above calculator to see for yourself. I'll use some numbers for a 138MHz antenna, with 5mm diameter coax. What you have are two loops, one smaller than the other. I spent some time trying to figure out just how it was supposed to work, before it finally clicked. And this page which describes the connections, and how impedance is matched.Ĭonstruction of the QFH antenna can be tricky to comprehend without seeing one, as the coaxial cables need to be connected at the right places, in the correct manner. I'll refer you to this website right away as it contains all the information you need, along with a calculator. The only disadvantage to this is marginal reduction in the antenna Q factor. A common choice is to use thick coaxial cable to construct the antenna, as it is easy to work with and cheap. It consists of two loops, which are run 90 degrees out of phase in order to produce circular polarization. The QFH is an omnidirectional, circularly polarized antenna (see below). In my opinion it seems more mechanically elegant, and easier to construct correctly, though this doesn't impact reception at all. Based on the opinions of those who have tried both, I opted for the QFH. The main two types of antenna used are the turnstile, and the Quadrifilar Helix Antenna (QFH) antenna.