Comments - The Musical and Chapter 1 of the Care and Feeding of Wireless Microphones - TheatreFace

Well Henry I stand doubly cor…

2011-01-11T17:34:36.895Z

Well Henry I stand doubly corrected. Teach me to write a response at home after the BSC Championship game...

Initially I was trying to avoid mentioning specific gear, but in order to be accurate and avoid another well deserved correction, I'll detail the what I'm using. I use 3-4 "UHF Antenna Distribution System"s (of various model numbers) manufactured by Shure for the discontinued UHF Shure wireless microphones we run. This year we replaced 12 of the UHF systems that were in the 700 MHz range. The new units (the Shure UR14D+) don't require a separate distribution unit as they're built into the receivers. With all of the above I run Shure UA870 active paddle antennas, and I have had great success with them. Both Shure's product support and my equipment dealer recommended staying with the active systems when we purchased the new units. I haven't encountered mixing or RF noise (outside of tuning to the wrong frequency) - but granted we are in a small TV/radio market area without a lot of high powered broadcasting.

Thanks again for your feedback.

Cheers,

Richelle

"I used the term 'powered ant…

2011-01-11T15:20:19.707Z

"I used the term 'powered antenna' completely inaccurately - coworkers and unfortunately I have called our passive paddles "powered" simply because they have a power light. So, 'powered antennas' is a complete misnomer - what I should've written was 'distributive antenna system.' "

If your antenna has a power light, it's because it has an active powered gain stage (amplifier) with the light indicating the presence of bias voltage which is required to power the circuit. This is most definitely a powered - and not a passive - antenna. A passive antenna has no bias voltage power indication since it's not required for the operation of the antenna.

"Distributive antenna system", actually 'distributed antenna system' or DAS, has little to no relevance here: A distributed antenna system is an RF signal propagation system employing many antennas (far more than the two associated with a single diversity system) and/or radiating coax deployed throughout a large area requiring coverage, usually on the order of multiple floors or building wide. Certainly DAS is sometimes deployed for large wireless intercom systems and more rarely for wireless microphone and IEM systems, but it is not the term applied to a diversity pair of [remote] antennas feeding a single wireless mic receiver or an antenna distribution unit (more accurately called a multicoupler).

With regards to your own frequency selection, although not what would be considered a comprehensive frequency coordination, your methodical approach (and yes, a bit of luck) seems to have served you well. I would suggest you have another spectrum sweep of your venue as many broadcasters have changed actual TV channels (especially from VHF to UHF) since the June 2009 DTV transition.

Henry Cohen

Production Radio Rentals

Hey Henry, Thanks for your…

2011-01-11T06:57:07.158Z

Hey Henry,

Thanks for your feedback! It's great to have response from a rental professional... I have worked at numerous theatres, but at the end of the day I work in a single facility with a specific set of gear. And, although I never claim to be the girl with all the answers I am offering advice.

You're comments especially remind me of one of the pitfalls of being a blogger, and that is being careful about terminology. I used the term "powered antenna" completely inaccurately - coworkers and unfortunately I have called our passive paddles "powered" simply because they have a power light. So, "powered antennas" is a complete misnomer - what I should've written was "distributive antenna system."

Another pitfall of the blogger is clarity. My point about using a remote antenna was NOT that they didn't need to be in line of site, but that they simply have a much smaller footprint than a rack full of wireless units. I wasn't trying to imply that a remote antenna has magical or mystical properties and can receive through 6 feet of concrete or 6 blocks away.

To answer your question about my own set up, I use what I mentioned - starting with the manufacturers recommendations for the model of mics we run. On top of the recommendations from (in this case Shure) I use a frequency sweep analyses that was done for our facility a few years ago. The sweep is a little dated, but it helps me avoid the major conflicts I have with local broadcasters etc. For this last show, I had to tune 12 of the units for the first time (units bought to replace the now banned 700 Mhz systems we had owned.) I started with the older units, checked all the mics and made sure nothing had changed or cropped up from the last use, fired up the other wireless devices we use (headsets, hearing impaired, etc.) then added the new units using the frequency scan feature, well - for 10 of the 12. The last two the frequency scan told me no clean channels. I had to manually find frequencies that had minimal cross reception - in both cases minimal enough that broadcast signal from the packs were strong enough to cancel out - then relegate them to the back-up channels to make sure. It maybe that I got lucky - but it was a painless, quick way to find the slots that were open. I worked one at a time, and left each unit on after frequency assignment. I didn't have any problems that impacted performance of the older or newer units.

Thanks again for you responce.

Cheers,

Richelle

"If you have the budget/renta…

2011-01-10T23:41:54.797Z

"If you have the budget/rental option to use powered antennas, do so . . ."

This is really *not* good advice. Powered antennas provide a non-linear juction where intermodulation distortion due to mixing can occur (compounding the mixing problems from any antenna distribution unit), as well as raising the RF noise floor and possibly pulling in unwanted RF energy from TV transmitters (and in short order, TVBDs). It's far better in most situations to use passive directional antennas (the typical non-powered log periodic dipole array - LPDA - aka "paddle" or "shark fin") with high quality, low loss coax of the appropriate size for the length required.

Furthermore, every wireless mic and IEM antenna deployment should strive for unobstructed line of sight to the bodypack, whether using the whip antennas on the mic receiver / IEM transmitter, or emloying remote antennas.

"Following reception, an absolute key to wireless performance is frequency selection." Excellent advice.

"Newer model wirelesses often have frequency scanning to check for open frequencies too. If they do, take advantage of the feature." Not very good advice. Using a receiver's scanning feature is pretty much a guarantee of IMD due to mixing. Proper frequency coordination when more than a few mics (two actually) is the only way to ensure no self-interference or mixing with other carriers.

I'm curious: How did you arrive at the frequencies you're using for your 30 wireless mics?

Henry Cohen

Production Radio Rentals