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Author Topic: Helical Antennae: RHCP/LHCP  (Read 7872 times)

Tim Steer

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Helical Antennae: RHCP/LHCP
« on: November 18, 2015, 04:50:43 am »

When setting up a wireless link using a transmitter and receiver with two helicals facing each other, should both antennas be RHCP or should I be using a LHCP/RHCP pair?

I'm sure this is a simple question to someone who knows about these things, but I'm afraid what I know about RF engineering could be written on the back of a napkin. From what I've gleaned from model aeroplane forums it sounds like both antennas should be identical, and choosing the wrong combination can result in a 30dB loss in received signal, but I wanted to get the opinion of some people in the industry, as one company I work for uses a RHCP/LHCP pair for wireless audio links (to my mind this intuitively 'seems wrong' as the 'threads' won't 'wind on' to each-other, if you catch my drift).

This begs the questions, what is the practical difference between RHCP/LHCP, and why might a company have equal numbers of both types in their hire-stock?
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Scott Helmke

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Re: Helical Antennae: RHCP/LHCP
« Reply #1 on: November 18, 2015, 09:57:14 am »

You want to use the same handedness / "sense" on both. Think of it like nuts on a threaded rod.

There is attenuation from the polarity mismatch when mixing the two types. A practical application might be putting IEM transmitters on LH and wireless mics on RH to reduce interference between the two.
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Pete Erskine

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Re: Helical Antennae: RHCP/LHCP
« Reply #2 on: November 18, 2015, 12:12:10 pm »

When setting up a wireless link using a transmitter and receiver with two helicals facing each other, should both antennas be RHCP or should I be using a LHCP/RHCP pair?

This brings up an interesting question.  Maybe Henry Cohen can answer.

If the 2 Helicals are facing each other should one be RH and the other LH for aligning the polarity?  Is the polarity mirror image?
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Keith Broughton

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Re: Helical Antennae: RHCP/LHCP
« Reply #3 on: November 18, 2015, 12:17:28 pm »

This brings up an interesting question.  Maybe Henry Cohen can answer.

If the 2 Helicals are facing each other should one be RH and the other LH for aligning the polarity?  Is the polarity mirror image?
Good question.
As for the OP, in a wireless link situation where antenna polarity can be fixed, is it worth using  helicals or would LP (fins) be fine?
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Mac Kerr

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Re: Helical Antennae: RHCP/LHCP
« Reply #4 on: November 18, 2015, 12:23:14 pm »

This brings up an interesting question.  Maybe Henry Cohen can answer.

If the 2 Helicals are facing each other should one be RH and the other LH for aligning the polarity?  Is the polarity mirror image?

Which way they are facing does not affect the polarization. As a point to point link they should have the same polarization (twist). To minimize cross interference between IEM transmitters and mic receivers they should have opposite polarization (twist).

Mac
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Tim Steer

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Re: Helical Antennae: RHCP/LHCP
« Reply #5 on: November 18, 2015, 12:36:59 pm »

You want to use the same handedness / "sense" on both. Think of it like nuts on a threaded rod.

There is attenuation from the polarity mismatch when mixing the two types. A practical application might be putting IEM transmitters on LH and wireless mics on RH to reduce interference between the two.

Thanks, that's how I imagined it to be.

Good question.
As for the OP, in a wireless link situation where antenna polarity can be fixed, is it worth using  helicals or would LP (fins) be fine?

I take your point, but it's a somewhat hypothetical situation that just interested me.

Which way they are facing does not affect the polarization. As a point to point link they should have the same polarization (twist). To minimize cross interference between IEM transmitters and mic receivers they should have opposite polarization (twist).

Mac

Makes total sense. Thanks everyone.
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brian maddox

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Re: Helical Antennae: RHCP/LHCP
« Reply #6 on: November 18, 2015, 02:48:07 pm »

Which way they are facing does not affect the polarization. As a point to point link they should have the same polarization (twist). To minimize cross interference between IEM transmitters and mic receivers they should have opposite polarization (twist).

Mac

The idea of thinking of it like a bolt really helped me visualize this.  But thanks for confirming that.

Oh, and how much fun is it to answer an RF question posed by Peter Erskine?  :)
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Henry Cohen

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Re: Helical Antennae: RHCP/LHCP
« Reply #7 on: November 19, 2015, 04:05:51 pm »

Oh, and how much fun is it to answer an RF question posed by Peter Erskine?  :)

Not nearly as much fun as when he asks at which BBQ place we should eat  ;D
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Mac Kerr

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Re: Helical Antennae: RHCP/LHCP
« Reply #8 on: November 19, 2015, 04:16:17 pm »

Not nearly as much fun as when he asks at which BBQ place we should eat  ;D

Big W's Roadside BBQ in Wingdale NY. I've already dragged Pete there, he cam away a believer.

Mac
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Steve M Smith

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Re: Helical Antennae: RHCP/LHCP
« Reply #9 on: November 19, 2015, 04:21:25 pm »

The idea of thinking of it like a bolt really helped me visualize this.  But thanks for confirming that.

I was going to suggest a length of threaded rod as an analogy. Rotate it 180 degrees and it is exactly the same.


Steve.
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