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Author Topic: Basic wireless coordination  (Read 2289 times)

Stephen Swaffer

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Basic wireless coordination
« on: October 26, 2015, 09:47:46 pm »

This may seem overly basic given some of the other topics on here, but we have to start with basics, right?

I have worked with sound for years in a church in a small town in a rural area.  We have typically run 2 Shure systems-currently using 2 Shure ULX systems and for a few years we have used 5 Line  handhelds.  RF coordination has been pretty simple.  The Shure  frequency locator list 5 TV stations-the closest 15 miles away the next some 40 miles away.

Once a year we have started renting a MiPro 8 channel system, though have used only 3-4 systems, but are moving to where we will use all 8, plus likely to rent a couple more Shure systems.  I know that, from a technical standpoint, there are more desirable ways to do what we do, but considering the constraints we face-budget/availability/location this seems to be our best option.  The MiPros typically come to me in complete disarray and I fight through getting enough to work to get through our production.  I'd like to actually have a plan of attack rather than just hoping to get lucky.

Manufacturers mention that channels too close may interfere.  How close is too close?

What is the purpose for groups of channels-it seems that the MiPro groups overlap frequencies?

Our media booth has roughly a 80 foot line-of-sight to stage and I do mean line of sight, not blocked by bodies at all-it is located about 12 feet above the auditorium floor. It seems very easy to get Rf reception, really just frequency coordination I am concerned about.  The only outside source that I feel like is a potential source of interference is a fast food restaurant across the street.  There is a second one roughly 1000 feet away.

Just looking for general guidelines-given this scenario how would you methodically approach setup?
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Steve Swaffer

Mac Kerr

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Re: Basic wireless coordination
« Reply #1 on: October 26, 2015, 10:07:51 pm »

I'd like to actually have a plan of attack rather than just hoping to get lucky.

Manufacturers mention that channels too close may interfere.  How close is too close?

What is the purpose for groups of channels-it seems that the MiPro groups overlap frequencies?

Our media booth has roughly a 80 foot line-of-sight to stage and I do mean line of sight, not blocked by bodies at all-it is located about 12 feet above the auditorium floor. It seems very easy to get Rf reception, really just frequency coordination I am concerned about.  The only outside source that I feel like is a potential source of interference is a fast food restaurant across the street.  There is a second one roughly 1000 feet away.

The first thing to do is get one of the free pieces of software that does frequency coordination. Both Shure and Sennheiser off free coordination software, and software is the only way to do it.

Anytime you have 3 or more transmitters, whether they are mic, wireless IEMs, or RF comms, you need to coordinate. Both Shure Wireless Workbench and Sennheiser SIFM have channel spacing specs built in as well as almost every RF mic, IEM or comm you are likely to run into. You tell the software where you are located so it can download the right information about TV channels and legally used frequency bands. Then once it knows what frequency bands you can use you start adding systems you want to use and have it suggest frequencies. You should start with the least agile systems, usually RF comms, then add your IEMs making sure that the software is set to its strictest standards. Lastly add your RF mics. If you cannot find enough frequencies for your mics you can turn off the strictest restrictions, like 3 transmitter intermods. Try again to you get enough frequencies. Pete Erskine has posted very clear and complete instructions HERE. I have made his posts stickies.

Mac
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Jeff Carter

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Re: Basic wireless coordination
« Reply #2 on: October 26, 2015, 10:20:51 pm »

Mac (who *is* one of the guys who does this for a living) has mostly pre-empted me but I'll post this anyway.

I see a whole bunch of different Mipro systems on their site, so the specific model numbers (or at least the frequency range) would help the guys who do this stuff for a living (I am not one of them) give better advice.

In addition to separating the operating frequencies you also need to be sure that no operating frequencies are too close to possible intermodulation products. RF transmitters are not entirely linear, which means that two bad things happen:
1. an isolated transmitter will also put out harmonics at multiples of the carrier frequency
2. A transmitter will also pick up RF emissions from nearby other transmitters (both carriers and harmonics) and non-linearity will mix those together to create intermodulated signal that will be sent out.

Second-order intermod is probably well outside the operating band (if you have two transmitters at f1=600 MHz and f2=610 MHz, for example, the second-order intermods are at f1+f2 = 1210 MHz and f1-f2=10 Mhz) but third-order intermods are trouble (that's stuff like 2*f1-f2 = 590 MHz... if you have a third mic at f3=590 MHz and transmitters 1 and 2 get close together, you've got problems).

The preset frequencies on the Mipro should in theory keep them from stepping on each other's intermods... but as soon as you drag in a few mics from somewhere else, well, there's a reason why frequency co-ordination software exists. I've only played a bit with Shure's Wireless Workbench but it works well enough for us when we need to co-ordinate our house gear with a few rentals.

A good link that came up for me on the Google is here. Mostly a conceptual description of intermod from the Shure site.
« Last Edit: October 27, 2015, 08:08:16 am by Jeff Carter »
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Tom Bourke

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Re: Basic wireless coordination
« Reply #3 on: October 26, 2015, 11:53:02 pm »

RF is part science and part art.  Shure WWB is a good starting point.  Be sure to feed into it ALL the info you have.  If you have any of the Shure products it can scan with use that too.  The same goes for any software your hardware supports.

Software can do theoretical models.  What it can't take into account is distance unit to unit and distance to other sources.  For example the largest show I have done had a couple hundred RF sources in WWB.  I had some fixed stuff I could not change.  It also had problems with some combinations I had present.  However I work in a space that is HUGE.  Almost to the point I could share frequencies at the extreme ends.

Software will help pick frequencies and show possible conflicts.  It is up to you to decide what is go or no go.  Always have it calculate back up frequencies so you have an easy list to go to should it be a problem mid show. In my space I keep a list of 5  alternative frequencies per band that any given tech can go to.
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Stephen Swaffer

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Re: Basic wireless coordination
« Reply #4 on: October 27, 2015, 10:21:32 am »

Mac (who *is* one of the guys who does this for a living)

I knew Mac was very knowledgeable in this area-this is one of the things I like about this forum-there are many guys who are very qualified in their field that are also patient enough to answer entry level questions.

Thank you to all who replied with very helpful info.  I will take time to look into the videos.  I enjoy where I live, but the nature of things is that I haven't found a way to get (reliable) high speed internet to my home, so I usually skip videos unless I know they are going to helpful.
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Steve Swaffer

ProSoundWeb Community

Re: Basic wireless coordination
« Reply #4 on: October 27, 2015, 10:21:32 am »


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