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[Russell Ault]

The conversation about audio polarity over in the LAB has got me pondering polarity in RF. Specifically, does the absolute polarity of an RF signal have any impact on the operation of, say, a wireless microphone receiver? If I hooked up a pair of baluns backwards in the RX antenna run (because...reasons, I guess?), would that cause reception issues?

Thanks!

-Russ

[Keith Broughton]

Considering that RF reception at, either of the receiving antennas, could be a combination of direct and (or)reflected signals, of a variety of polarities, I would think that absolute polarity is not an issue.

[Kevin Graf]

The Radio Frequency is the carrier, it's not the audio signal. The audio is either Frequency Modulated analog, or it's digital date.
Now if the RF is a combination of direct and (or)reflected signals, of a variety of polarities, then there can be reception problems. Like in car radio FM there is the 'picket fence' problem.

[John Roberts {JR}]

 

JR

[Henry Cohen]

The conversation about audio polarity over in the LAB has got me pondering polarity in RF. Specifically, does the absolute polarity of an RF signal have any impact on the operation of, say, a wireless microphone receiver? If I hooked up a pair of baluns backwards in the RX antenna run (because...reasons, I guess?), would that cause reception issues?

Are you asking about the polarity of the RF signal while still in the electrical domain (current through coax), in the electro-magnetic domain (radio waves in space) or at the energy conversion point in the transducer (antenna)?

In the coax: If you can fully isolate the signal in the transmission line, through a transformer, you should be able to "flip" the polarity in an analog wireless mic system with only the loss through the transformer being the primary concern, as long as there is no connection of the shield to the counterpoise at the antenna. With a digital system however I believe that may effect the constellation pattern and thus the signal would not be recovered. (Don't try this with a full powered AM broadcast transmitter; more than just the earthworms would be upset.)

In space: Flipping polarization (0° to 180°) should not be an issue; cross-polarization of 90° however is mathematically a complete null and loss of signal. So here the question is what consitiutes opposite polarization; 180°, or is it horizontal vs. vertical?

At the transducer (antenna): see above.

[Russell Ault]

Are you asking about the polarity of the RF signal while still in the electrical domain (current through coax), in the electro-magnetic domain (radio waves in space) or at the energy conversion point in the transducer (antenna)?

In the coax: If you can fully isolate the signal in the transmission line, through a transformer, you should be able to "flip" the polarity in an analog wireless mic system with only the loss through the transformer being the primary concern, as long as there is no connection of the shield to the counterpoise at the antenna. With a digital system however I believe that may effect the constellation pattern and thus the signal would not be recovered. (Don't try this with a full powered AM broadcast transmitter; more than just the earthworms would be upset.)

In space: Flipping polarization (0° to 180°) should not be an issue; cross-polarization of 90° however is mathematically a complete null and loss of signal. So here the question is what consitiutes opposite polarization; 180°, or is it horizontal vs. vertical?

At the transducer (antenna): see above.

The electrical domain is the one I was most curious about. My understanding of polarity in the EM domain is that it's...complicated (pondering the concept of "circular polarization" still gives me the odd headache), but in the electrical domain it seems like it should be a relatively-straightforward discussion (voltage can only be plus or minus, right?). In my head, it would make sense that any signal with a carrier would be electrical-polarity agnostic, but I wasn't sure about how digital modes (or even something like suppressed-carrier SSB) would fare.

I feel like part of the answer to my question involves this thought experiment:
Let's say we have two dipole antennas, one to transmit a signal and the other to receive it. Both antennas are mounted vertically in an RF-anechoic environment, but one of them is "upside-down" relative to the other. Will the signal coming out of the RX antenna have the same electrical polarity as the signal going into the TX antenna, or the opposite?

-Russ

[Steve-White]

Dang Russ, sorry I started that thread now....  JK!

For RF, there is a carrier and the signal is modulated (superimposed into) at the source and demodulated at the destination.  Because the signal is a component of the carrier energy and is stripped away, the result puts things in the time domain with regard to phase or polarity of the original signal.

The RF carrier is much higher frequency or bandwidth than the audio.

For this part, I'll probably get into trouble attempting to articulate a proper response, but here goes anyway:

"I feel like part of the answer to my question involves this thought experiment:
Let's say we have two dipole antennas, one to transmit a signal and the other to receive it. Both antennas are mounted vertically in an RF-anechoic environment, but one of them is "upside-down" relative to the other. Will the signal coming out of the RX antenna have the same electrical polarity as the signal going into the TX antenna, or the opposite?"

Orientation of antenna's relative to the source is pretty complex.  Given the very short wavelengths involved.  Consider your cell phone with regard to the tower it's sync'd up to as you move your head about or the radio in a vehicle as it moves along, or an aircraft radio as it moves along.

Why, somebody with knowledge in physics or electrical engineering may be able to articulate that - I can't beyond that it doesn't matter.

I suppose at some velocity the doppler effect would apply to the RF signal(s) too - not sure if anything we have today is fast enough for that phenomenon.  That's how the astronomers determine object movement in space relative to earth, look at the color of the light emitted.

Hope I don't get hammered too hard, but ya gotta hang it out there and take one on the chin every now and then. 

With regard to dual antenna's as it applies to our audio equipment - diversity is probably the answer there - any audio equipment that uses two antenna's at the receiver - the receiver picks the one with the best signal and uses it - always a case of either and never both.

EDIT: Above was the way it worked, not anymore.  See below. 

[Henry Cohen]

I feel like part of the answer to my question involves this thought experiment:
Let's say we have two dipole antennas, one to transmit a signal and the other to receive it. Both antennas are mounted vertically in an RF-anechoic environment, but one of them is "upside-down" relative to the other. Will the signal coming out of the RX antenna have the same electrical polarity as the signal going into the TX antenna, or the opposite?

I actually do this fairly regularly, and I've never had the ME or BE note the vocals or instruments on RF were out of polarity; I'll ask next time.

[Henry Cohen]

. . . any audio equipment that uses two antenna's at the receiver - the receiver picks the one with the best signal and uses it - always a case of either and never both (emphasis added).

Not so: Many modern high end digital systems (Axient, and IIRC Sennheiser S6000 & S9000) use maximum ratio combining, taking the best bits from each antenna to reconstruct the data stream. No switching involved. COFDM RF video transmitters (for handheld cameras) have been doing this for many years, with up to eight antennas per receiver.

Sorta' like your friend's fuzzy ears 

[Steve-White]

Not so: Many modern high end digital systems (Axient, and IIRC Sennheiser S6000 & S9000) use maximum ratio combining, taking the best bits from each antenna to reconstruct the data stream. No switching involved. COFDM RF video transmitters (for handheld cameras) have been doing this for many years, with up to eight antennas per receiver.

Sorta' like your friend's fuzzy ears 

RF knowledge base is a bit dated I see - thx!

[ProSoundWeb Community]