Phasing lines for 2-m Yagi circular polarized project
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 link.
Request ideas, guidance, advice, comments, please.
73
Dave N4CVX
Sent from my iPad
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 Figures" for more information on that gave me the two pertinent links below:
https://en.wikipedia.org/wiki/Lissajous_curve https://www.youtube.com/watch?v=t6nGiBzGLD8
On Fri, Feb 10, 2017 at 8:30 AM, Dave Mann cwo4mann@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 link.
Request ideas, guidance, advice, comments, please.
73
Dave N4CVX
Sent from my iPad _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
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
Sent from my iPad
On Feb 10, 2017, at 12:00, John Toscano tosca005@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 Figures" for more information on that gave me the two pertinent links below:
https://en.wikipedia.org/wiki/Lissajous_curve https://www.youtube.com/watch?v=t6nGiBzGLD8
On Fri, Feb 10, 2017 at 8:30 AM, Dave Mann cwo4mann@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 link.
Request ideas, guidance, advice, comments, please.
73
Dave N4CVX
Sent from my iPad _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Hi. Here is a very fine page describing almost "everything", also calculator. http://www.dg7ybn.de/Building/xpol.htm
73, Paul
________________________________________ From: AMSAT-BB amsat-bb-bounces@amsat.org on behalf of Dave Mann cwo4mann@comcast.net Sent: 10 February 2017 15:30 To: amsat-bb@amsat.org Subject: [amsat-bb] Phasing lines for 2-m Yagi circular polarized project
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 link.
Request ideas, guidance, advice, comments, please.
73
Dave N4CVX
Sent from my iPad _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
participants (3)
-
Dave Mann -
John Toscano -
LB2TG Paul