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Author Topic: Effects of cross polarization on 432??  (Read 3693 times)
VA3ELE
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Posts: 5




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« on: October 26, 2012, 09:09:29 PM »

Does anyone here know what the effects of cross polarization are on 432MHz?
for example working from  horizontal to vertical or horizontal to circular polarization (left or right)?

thanks in advance for any replies

73 de VA3ELE
Peter
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KQ6EA
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Posts: 609


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« Reply #1 on: October 26, 2012, 09:58:14 PM »

It will be the same as cross-polarization on other VHF/UHF bands.
Theoretically, you'll have infinite loss between the two polarizations.
In practice, it can be anything from a few dB to 25 or more dB.
A lot of what happens will depend on the path between the two stations. If there are obstacles or things that will reflect the signals between the two stations, then the polarization will get flipped and flopped along the path, and the amount of loss will be hard to predict.
If you were out in space, you'd be closer to a true 'line of sight' path, and you'd see much higher loss between the two polarizations.

Jim
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KA4POL
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Posts: 1985




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« Reply #2 on: October 26, 2012, 10:17:31 PM »

For FM vertical polarization will be the way to go. However, usually when the RF is reflected the polarization changes. So the result will be somewhere between horizontal and vertical. This is why actually a circular polarized antenna might be the best solution depending upon where you are living, i.e. mountains of flat land.
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WB6BYU
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Posts: 13253




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« Reply #3 on: October 27, 2012, 06:32:25 AM »

The loss between linear polarization (horizontal, vertical or slant) and circular is
3dB.

The loss between clockwise circular and counterclockwise circular is theoretically
infinite.  Just as with horizontal and vertical, reflections can change the relative
levels and reduce that.

For moonbounce, where the signal reflects off of a (nominally) single object,
a signal that goes up clockwise will come back counterclockwise due to
the reflection.
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WB2WIK
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Posts: 20595




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« Reply #4 on: October 27, 2012, 09:02:46 AM »

I've found polarization "holds" very well on the VHF-UHF-SHF bands over almost any kind of terrain, as long as the path is tropospheric.  On 432 MHz, it's all tropospheric except for working satellites or moonbounce, and even those are line of sight paths.

I can work a station 300 miles away on 432 MHz SSB and if I switch from horizontal to vertical polarization using similar antennas for each, I can completely lose a station who started out S9 with the proper (horizontal) polarization.  And I don't have any line-of-sight paths for 300 miles, it's always over rugged terrain.


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KA4POL
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Posts: 1985




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« Reply #5 on: October 27, 2012, 09:10:57 AM »

Just to mention it. Going through the ionosphere will also change polarization. The effect is called Faraday rotaion. So do not expect a perfect change as proposed by theory.
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WB2WIK
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« Reply #6 on: October 27, 2012, 06:20:45 PM »

Just to mention it. Going through the ionosphere will also change polarization. The effect is called Faraday rotaion. So do not expect a perfect change as proposed by theory.

Unless you're working moonbounce, that won't happen on 70cm. Wink
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KA4POL
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Posts: 1985




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« Reply #7 on: October 27, 2012, 11:05:12 PM »

Just to mention it. Going through the ionosphere will also change polarization. The effect is called Faraday rotaion. So do not expect a perfect change as proposed by theory.

Unless you're working moonbounce, that won't happen on 70cm. Wink

Really?  Grin

As BYU mentioned the moonbounce change in polarization I deemed it helpful for completeness sake. These effects are not commonly well known.
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VA3ELE
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Posts: 5




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« Reply #8 on: October 31, 2012, 05:20:43 PM »

Thank you for the replies guys.
I have no problem working stations 300+miles. Just recently had encountered the dilemma where I was trying to work a station that was 440miles away, but the other op was running circular polarization. We tried SSB and CW with no luck. After several nights of trying we decided it was time for a marathon run using JT65b.
We sat and actively watched the screens and listened for tones, after many hours it was time for some sleep. Waking up ocassionaly to check for decodes after about 4hrs came the first decode... After switching TX to the next one I went back to sleep. After a few more hours I woke up again to finally see a decode from the other station.  By the time we were satisfied with proper decodes it was a 14hr contact!

It seems to have taken very good QSB peaks of proper duration to get proper decodes.
It led me to the question, how much attenuation was there since I ran horizontal and opposing station ran circular polarization.

Thanks again for the replies

73 de VA3ELE
FN03dm

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WB2WIK
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« Reply #9 on: November 01, 2012, 11:07:10 AM »

Just to mention it. Going through the ionosphere will also change polarization. The effect is called Faraday rotaion. So do not expect a perfect change as proposed by theory.

Unless you're working moonbounce, that won't happen on 70cm. Wink

Really?  Grin

As BYU mentioned the moonbounce change in polarization I deemed it helpful for completeness sake. These effects are not commonly well known.

You misinterpreted what I meant (maybe I stated it poorly).

"That won't happen on 70cm" didn't refer to working moonbounce -- I've worked e.m.e. on 70cm since the late 1970s.  I meant, "unless you're making contacts via moonbounce," the Faraday rotation won't occur (via normal tropospheric paths, even if they are hundreds of miles over the horizon).
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