[amsat-bb] Re: Testing a UHF antenna

normn3ykf at stny.rr.com normn3ykf at stny.rr.com
Sat Jan 21 15:02:42 PST 2012

Thank you so much for sending the article on your experiments in the 2400MHz band. The author of the page does provide some information on connecting the infinite balun. 
It's here: http://jcoppens.com/ant/qfh/img/v2/012.jpeg
He also does provide a clue of performance of inverse connection of the loops in simulation 
here: http://jcoppens.com/ant/qfh/sim.en.php It's in the n'th column labeled as .44inv

Re the meter and the cable: I need to find some connectors so that I can make up a cable. Just finished a move and am still in the process of decimating the boxes. 

Will report back when I get a cable made. 
73 de Norm n3ykf

> 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

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