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Author Topic: IEM distribution antenna / combiner  (Read 1803 times)

Lyle Williams

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Re: IEM distribution antenna / combiner
« Reply #30 on: June 20, 2014, 04:13:32 am »

In considering the impact on systems, the dominance of FM modulation in wireless mics/iems and the FM capture effect needs to be taken into account.  Even if an IM product lands of a frequency you are using, if it is >20dB down in strength from your carrier you aren't going to hear it.

It is good to be aware of this stuff, and run through a planning cycle to get a feel for how the numbers fall out.  If you go to the trouble of putting 30mW mics and iems into the model, make sure you put the 2-5w UHF handheld crew radios in too.  See what adding a signal 20+dB hotter does to the numbers.

That said, lots of gear works faultlessly every day without those users being remotely aware of this issue.

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Steve.Oldridge

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Re: IEM distribution antenna / combiner
« Reply #31 on: June 20, 2014, 10:03:42 am »

That said, lots of gear works faultlessly every day without those users being remotely aware of this issue.

I'd say we fall right into that group :)
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Debbie Dunkley

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Re: IEM distribution antenna / combiner
« Reply #32 on: June 20, 2014, 10:12:36 am »

I think one of the reasons I have few issues is because I keep the transmitters in a rack on stage within a few feet of the packs.
I forgot to mention that the main band I use the iems with has wireless mic, wireless guitar and wireless bass also. Wow….so I suppose I do have some stuff going in the RF realm really. But if there is some interference going on up there, it has never been apparent to me.
I have recorded these sessions too and nothing shows up bad there either. Just lucky I suppose. Did some reading on this and trying to understand the science behind it all……oh look……..gotta spend more money….yay…  :-\
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

Pete Erskine

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Re: IEM distribution antenna / combiner
« Reply #33 on: June 20, 2014, 10:48:22 am »

Is it necessary to "profile" and adjust settings for each venue - assuming local radio/tv interference intensity will likely vary ?

I always start with a scan of the venue environment, both outside and inside.  The FCC database is not always up to date but if it lists a DTV channel which you cant see its always better to assume it might come on at any time.  Inside scans are useful since often the building shields you from TV stations and that channel can be used since it cannot be received in your location.

In IAS the scan can be imported in a graph which shows your frequencies.  This scan I did with the TTI PSA2702 Spectrum analyzer whic is a mid range cost analyzer, about $2000.  The Yellow channels are marked as DTV.  The blue lines are my frequencies.

Here are 2 scans I took this week in midtown NY.  The first is outsice the venue and the second is inside.  Regardless of the shielding, I do not use the clearer DTV channels unless I have a particularly heavy coordination.

Please visit my webpage on RF coordination.  Best Audio Frequency Coordination.  The RF Coordination for Roadies manual might answer a lot of your questions
« Last Edit: June 20, 2014, 10:52:47 am by Pete Erskine »
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Jerome Malsack

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Re: IEM distribution antenna / combiner
« Reply #34 on: June 20, 2014, 11:33:11 am »

Debbie another thing to look at might be the DTV stations in your area. 

http://www.antennaweb.org/

put in you zip and see what stations / channels / frequencies are in use.  You will want to avoid the used TV bands. 
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Debbie Dunkley

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Re: IEM distribution antenna / combiner
« Reply #35 on: June 20, 2014, 12:19:59 pm »

Debbie another thing to look at might be the DTV stations in your area. 

http://www.antennaweb.org/

put in you zip and see what stations / channels / frequencies are in use.  You will want to avoid the used TV bands.

Thanks Jerome..I checked it out but it shows channel numbers - not frequencies.
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

Pete Erskine

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Re: IEM distribution antenna / combiner
« Reply #36 on: June 20, 2014, 12:29:31 pm »

Thanks Jerome..I checked it out but it shows channel numbers - not frequencies.

Plug channel numbers into FREE Channel guide RF Planning spreadsheet and see where your equipment falls.

http://www.bestaudio.com/_private/downloads/channels.zip
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brian maddox

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Re: IEM distribution antenna / combiner
« Reply #38 on: June 20, 2014, 01:13:53 pm »

Just to kind of sum things up... 

[and for the record this post is not addressed to any of the posters directly.  just some general thoughts]

It is entirely true that you can run multiple wireless mice and IEMs and not have a problem without ever coordinating the frequencies.  It's also true that you can fly a plane across the country without a radio, transponder or instruments and not hit anything.  This phenomenon is what is known as luck.  i for one prefer a slightly safer method of travel.

In today's world of shrinking available RF bandwidth, the odds of you getting lucky are literally growing longer by the day.  That's why frequency coordination is coming out of the realm of high end professionals and into the realm of the weekend warrior.  Welcome to the modern age.

If you are running ANY wireless units and are not using coordination software you are asking for trouble.  And the chances of trouble happening are going to continue to grow.  We live in a fantastic time where coordination software is free [it used to be VERY expensive] and relatively easy to use.  If you're currently relying on the flying blind technique, do yourself a favor, take a few minutes and learn how to use it.  The show you save could be your own....
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Debbie Dunkley

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Re: IEM distribution antenna / combiner
« Reply #39 on: June 20, 2014, 01:15:38 pm »

You clever peeps…thank you.
I was able to check out frequencies for tonights show. According to what I can make out, I have 2 local channels that fall into band G for me. Both however are at the very ends of the spectrum and the ones I use are right in the middle (ish)…… I hope I am understanding correctly???
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."
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