Hi all. Am in the process of building a quadrifiliar helix antenna using this
page: http://jcoppens.com/ant/qfh/calc.en.php .
How much cable should I use between the device under test and the antenna
analyzer? I've got a Times T-100
73 de Norm
Hi Norm
I was looking at http://jcoppens.com/ant/qfh/calc.en.php .
but unfortunately there are not informations on how to connect the 4 by 1/2 wavelength loops to get End-Fire or Back-Fire radiation from the quadrifiliar helix antenna as well no information to get a 50 ohm match properly connecting the 4 terminals of the loops to the infinite balun so that I suggest you to read the article:
"Experimental Investigation of Quadrifilar Helix Antennas for 2400 MHz" published into the AMSAT-Journal May-June 2004
BTW, about your question the lenght of coax cable between the device under test and the antenna analyzer must be any even or odd numbar of 1/2 electrical waveleght of coax cable for the frequency in use where the 1/2 electrical wavelenght of the coax cable is the 1/2 free wave multiplied by the velocity factor Vf of the coax used i.e.Vf = 0.66 for RG-213
When the lenght of any transmission line is 1/2 electrical waveleght the impedance at one end of it is the same at the other end of it i.e. the impedance of the antenna will be seen unchanged at the antenna analyzer input connector no matter the value of the VSWR.
73" de
i8CVS Domenico