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Author Topic: Reversed Dipole Polarity  (Read 2580 times)

Russell Ault

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Reversed Dipole Polarity
« on: April 16, 2016, 03:08:06 pm »

Hi all!

This should be a fairly straight-forward question: can reversing the polarity of a vertically-oriented 1/2-wave omni dipole antenna cause RF (or AF) problems? For example, if I mount one (of a diversity RX pair) A1031-U antenna "upside-down", will the cause reception/diversity/AF production issues?

Thanks!

-Russ
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Pete Erskine

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Re: Reversed Dipole Polarity
« Reply #1 on: April 16, 2016, 03:11:16 pm »

Hi all!

This should be a fairly straight-forward question: can reversing the polarity of a vertically-oriented 1/2-wave omni dipole antenna cause RF (or AF) problems? For example, if I mount one (of a diversity RX pair) A1031-U antenna "upside-down", will the cause reception/diversity/AF production issues?

Thanks!

-Russ

No issue.  Wonder if Audio will be upside down too?
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Russell Ault

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Re: Reversed Dipole Polarity
« Reply #2 on: April 16, 2016, 03:13:17 pm »

No issue.  Wonder if Audio will be upside down too?

Thanks, Pete! I honestly wasn't sure if reversing the polarity of the antenna would reverse the polarity of the audio or not. Still have a lot to learn...

-Russ
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Scott Holtzman

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Re: Reversed Dipole Polarity
« Reply #3 on: April 16, 2016, 04:17:53 pm »

Thanks, Pete! I honestly wasn't sure if reversing the polarity of the antenna would reverse the polarity of the audio or not. Still have a lot to learn...

-Russ

When you say the polarity of the antenna normally you are speaking of the angle of radiation relative to the ground plane.

Indeed there is signal loss if the radiation source and the receiving antenna do not arrive at the same angle.  Less induction occurs and a reduction in signal proportional to the difference in polarization.

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Scott AKA "Skyking" Holtzman
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Russell Ault

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Re: Reversed Dipole Polarity
« Reply #4 on: April 16, 2016, 04:37:08 pm »

When you say the polarity of the antenna normally you are speaking of the angle of radiation relative to the ground plane.

Indeed there is signal loss if the radiation source and the receiving antenna do not arrive at the same angle.  Less induction occurs and a reduction in signal proportional to the difference in polarization.

Right, so, in this particular case, I was wondering what would happen when a radiation source arrives at an antenna that is effectively 180 degrees "out". My understanding is that this causes no attenuation, but in the case of a dipole (or any "balanced" antenna), I was wondering if it might cause other effects.

Thanks!

-Russ
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Jason Glass

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Re: Reversed Dipole Polarity
« Reply #5 on: April 16, 2016, 08:44:41 pm »



When you say the polarity of the antenna normally you are speaking of the angle of radiation relative to the ground plane.

Indeed there is signal loss if the radiation source and the receiving antenna do not arrive at the same angle.  Less induction occurs and a reduction in signal proportional to the difference in polarization.

Hi Scott,

Actually, the angle of radiation is the description of polarization, rather than polarity. In the OP's case, a 180 degree rotation of linear polarization is a rare case where the term reversed polarity is coincidentally correct.  ;-)

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Scott Holtzman

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Re: Reversed Dipole Polarity
« Reply #6 on: April 17, 2016, 01:50:25 am »


Hi Scott,

Actually, the angle of radiation is the description of polarization, rather than polarity. In the OP's case, a 180 degree rotation of linear polarization is a rare case where the term reversed polarity is coincidentally correct.  ;-)

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Jason, since the RF connection is not balanced was the OP's question what happens if the shield is connected to the radiating element of the antenna?

My comment was more pedestrian, if a basic yagi is rotated 90 degrees there is quite a bit of loss.  Frankly I could not find the correct function on a quick search to calculate the loss or I would not have spoken so generically.

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Jason Glass

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Re: Reversed Dipole Polarity
« Reply #7 on: April 17, 2016, 11:22:00 am »

Jason, since the RF connection is not balanced was the OP's question what happens if the shield is connected to the radiating element of the antenna?

My comment was more pedestrian, if a basic yagi is rotated 90 degrees there is quite a bit of loss.  Frankly I could not find the correct function on a quick search to calculate the loss or I would not have spoken so generically.
Hi Scott,

I'm sorry; I must have misunderstood the OP.  Swapping the coax conductor with shield should indeed reverse a dipole's polarity. Although the coax feed line is unbalanced, a dipole is inherently balanced, so a well designed example will include some sort of balun to match impedance and suppress current on the coax shield.

Regarding polarization mismatch losses, the formula for polarization loss factor is cos(a)^2, where (a) is the mismatch angle in degrees.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Russell Ault

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Re: Reversed Dipole Polarity
« Reply #8 on: April 17, 2016, 01:13:21 pm »

I'm sorry; I must have misunderstood the OP.  Swapping the coax conductor with shield should indeed reverse a dipole's polarity. Although the coax feed line is unbalanced, a dipole is inherently balanced, so a well designed example will include some sort of balun to match impedance and suppress current on the coax shield.

Hi Jason!

I think you understood my question perfectly, it just turns out not to have been a particularly smart question. :P

My fear was that taking a balanced antenna and switching the "hot" and "cold" ends (as seen at its balun) by flipping it upside-down would have the same effect as switching the hot and cold connections in a balanced audio circuit. Sounds like the answer is a resounding "no".

Thanks all!

-Russ
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