Causes of RF breakup - cars in parking lots, metal bracelets worn by talent?

[Ty Ford]

Two questions for the group….

 

Have you ever noticed that wireless reception gets less reliable when you're shooting outside in a parking lot full of cars? I had this happen once a while back and it stuck in my head. Wonder why?

 

We were moving with booms at the same time and had the receivers and mixers in our bags. My thought was that with all that car metal for the RF to bounce off of, the signal was arriving at the receiver at different times (multipath) and that caused the breakup.

 

And while I'm on the topic of metal and breakup, has anyone noticed a correlation between the number of clangy metal bracelets worn by the on-camera talent and wireless breakup of her or anyone else's wireless lav?

 

Regards,

 

Ty Ford

[Nate C]

I have definitely noticed reduced range when cast get between cars/large metal thingy's and me. With line of sight in car parks I have felt like I should be getting better reception then I was, but never to a level that I had to hit the panic button. IF outputting at a higher MW, say 250 over 50, than multi path issues could arise in this kind of environment. I live in Australia where we are restricted to 100mw so this mainly theory over real world results.

 

AS for clangy jewellery the main issue I have had is the clangy. I did have a woman with a giant ugly neck piece that I seemed to get less than average reception. But yet again I have no scientific proof and the transmitter was no near the neck piece.   

[Reinout Weebers]

I think you already answered the question. Multi path, out of phase signals don't do reception any good. Human bodies, I see them as big sacks of water don't help either. So, I put my di-pole antennas on a boompole and try to get a direct line of sight from above. A regular boompole will reflect as well, so I made a little wooden divider witch gives a meter wide span. I can imagine you'll get even better results with directional antennas. Btw, in the Netherlands we're restricted to 50mW transmitters.

Sent from my iPhone using Tapatalk

[Geoff Tirrell]

I would add walls to the list not your normal wooden stud residential walls.. as while they will reduce your signal some they will not cancel it.  I am talking about the steel stud jobs they use in hospitals and business.  

[LarryF]

Multipath is not your friend. Reflections from cars in parking lots is such a problem that our walk area for new products is the upper parking lot at Lectro. There is an area about 35 feet from transmitter to receiver that is affectionately referred to as The Zone Of Death, caps intended. It's like the Sargasso Sea for RF but it's not a myth. We have instrumented the reception there and signal levels jump up and down 60 dB. Often the change in RF level is so quick, you don't even see it on the receiver display but you do hear the glitch.

Best Regards,
Larry Fisher
Lectrosonics

[Derek Mansvelt]

Straying slightly off topic but still in the RF zone, has anyone else ever experienced a shortening of range when working in a high humidity area. I occasionally work in a city in my country that is known for its high levels of humidity and often have a drop in range that I believe may be caused by the extra moisture in the air. This also happens when we work right next to the sea with big spay from waves. Of course I could be completely wrong?

That 35ft Zone of Death is good to know about Larry, I may move further from set in future

[LarryF]

Straying slightly off topic but still in the RF zone, has anyone else ever experienced a shortening of range when working in a high humidity area. I occasionally work in a city in my country that is known for its high levels of humidity and often have a drop in range that I believe may be caused by the extra moisture in the air. This also happens when we work right next to the sea with big spay from waves. Of course I could be completely wrong?

That 35ft Zone of Death is good to know about Larry, I may move further from set in future

Hi Derek,

I have not heard of moisture in the air reducing range except for much higher frequencies from satellites such as Dish and DirectTV and then in heavy snowfall or rain. If moisture played a big part, there would be a lot literature about the subject.

 

The 35 foot distance has little to do with the multipath problems. If we moved the receivers a hundred feet away, the problem would be worse. It just is that at 35 feet on our walk test, the transmitter is right among the cars, pickups and SUV's. Going farther away won't help.

Best Regards,

Larry Fisher

Lectrosonics

[Derek Mansvelt]

Hi Larry

Pity! I was hoping to have an excuse to get closer to the car, and therefore home. 

Ok so I guess Im wrong about the moisture. As with most RF problems it would be great to have an answer and therefore a possible solution to every problem but thats the way it goes some days.

[studiomprd]

nateC: " IF outputting at a higher MW, say 250 over 50, than multi path issues could arise in this kind of environment. "

it is not the power level that creates the multi-path issues, though sometimes higher power exacerbates the issues...

 

and yes, some places, like car lots, have more multi-path issues than others

Edited December 9, 2014 by studiomprd

[RadoStefanov]

Modern mixers don't care about an occasional drop out in tough environment.