[amsat-bb] Phasing lines for 2-m Yagi circular polarized project

Dave Mann cwo4mann at comcast.net
Fri Feb 10 23:02:07 UTC 2017

```Thank you John, it's all clear to me now.  I just hooked a couple of pieces of coax to my o'scope and sure enough I saw that Lissajous pattern.  Clever, that Frenchman!

Best 73
Dave N4CVX

> On Feb 10, 2017, at 12:00, John Toscano <tosca005 at umn.edu> wrote:
>
> I presume that you know that to get circular polarization, one set of
> elements needs to be electrically 1/4 wavelength ahead or behind the other
> set of elements. So if one line was 1/2 wavelength long, the other line
> would be 1/4 wavelength or 3/4 wavelength long, if the horizontal and
> vertical elements were at exactly the same spot on the boom. The more
> common method is to set the vertical and horizontal elements at 1/4
> wavelength different locations on the boom, and then you only need two
> feedlines that are exactly the same length. The advantages there include
> the fact that phasing lines' lengths need to take account of the velocity
> factor of the coax, whereas placing elements at different boom locations is
> equivalent to a velocity factor of 1.0 (air).
>
> So how to get the two feedlines exactly equal? Besides lining them up
> side-by-side when cutting them, you can connect one end of the cables to a
> 2-port power divider (or a simple T connector if you aren't worried about
> an impedance bump to your signal source), and the other ends of the cables
> to the X and Y inputs of an oscilloscope that has X-Y plotting capability.
> For two equal lengths, you should get a perfect diagonal line, and if one
> cable is a bit longer than the other, you will get a long, slender,
> diagonal ellipse. If the cables differ by a full 1/4 wavelength (or 3/4
> wavelength), you would get a perfect circle. If the cables differ in length
> by exactly 1/2 wavelength, you would get a perfect diagonal line with the
> opposite tilt direction as the zero-difference tracing. Googling "Lissajous
>
> https://en.wikipedia.org/wiki/Lissajous_curve
>
>> On Fri, Feb 10, 2017 at 8:30 AM, Dave Mann <cwo4mann at comcast.net> wrote:
>>
>> I have prepared my 2-m yagis.  Now ready to set them up to use on the
>> birds.  I'm thinking setting one horizontally and the other vertically,
>> spaced about 1 ft apart on a boom.  Now, how to measure the coax and
>> connect them for circular polarization?
>>
>> FYI, when all set up, I'll put the project details on my Dropbox with a
>>
>>
>> 73
>>
>> Dave N4CVX
>>
>>
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