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Author Topic: EME and spatial + faraday rotation  (Read 777 times)
WD4ELG
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Posts: 875




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« on: August 03, 2012, 11:08:02 PM »

Been doing some reading on this topic. 

Here's a summary of my first successes last night and early this morning on 144 EME:

* 2M9SSB in front yard, HL350VDX, IC910H, WSJT 9.1, 350W, 50 foot of LMR400 from DX Engineering
* PA0JMV heard me one-way from 0245 to 0330, best -26 on my signal.  I never copied him
* I worked ES6RQ, heard him initially then he faded, he switched to V pol and we completed QSO
* I1ANP reported hearing me on a single horiz yagi on his end, one-way prop
* RK3FG reported one way prop, best -27 on my sig, I never copied him
* I worked PA2CHR AFTER I rotated my antenna by hand to -60 degrees (per MoonSked recommendations). 
* I heard OZ1LPR but he did not hear me, with my antenna at -60 degrees (per Moonsked recommendations)


My question:  just how much will an antenna like M2 2XP20 help me?  How exactly does it switch between H and V?  Or are there separate coax lines needed for each polarity?


Mark Lunday
WD4ELG
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K2DC
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Posts: 1365


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« Reply #1 on: August 04, 2012, 03:01:11 AM »

Mark,

   The manual for the M2 isn't specific, but it implies that any pol switching is by user-supplied relays.  It's either that, or two separate feedlines all the way up.

73,

Don, K2DC
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WB6BYU
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Posts: 13287




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« Reply #2 on: August 04, 2012, 06:22:38 AM »

Typically with crossed yagis each has its own feedpoint, and polarity is switched by
feeding one or the other, or both with various lengths of coax for each.

For two antennas in the same relative position, the 6 typical combinations would be
something like this:

vertical:  just vertical yagi
horizontal:  just horizontal yagi
right 45 degree slant:  vertical + horizontal at 0 degrees
left 45 degree slant:  vertical + horizontal at 180 degrees
right circular:  vertical + horizontal at +90 degrees
left circular:  vertical + horizontal at -90 degrees

(the details of right and left may be reversed due to how the antenna is built, but
the concept remains the same.)

The phase shifts can be accomplished with lengths of coax, or by offsetting the feedpoint
spacially.   This antenna already has the feedpoints offset by 90 degrees, so feeding the
two antennas in phase will give circular polarization.

This switching is usually done by a set of relays at the antenna with a single feedline
to the shack, but you can also run separate feedlines and do the switching in the shack.
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WD4ELG
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Posts: 875




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« Reply #3 on: August 04, 2012, 07:43:56 AM »

Thanks for that detailed info.  NOW I understand how this antenna works.  Much appreciated.  73

WD4ELG
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