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Author Topic: IEM distribution antenna / combiner  (Read 17165 times)

Debbie Dunkley

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IEM distribution antenna / combiner
« on: June 14, 2014, 07:37:11 pm »

Just wondering about these .....
I have 2 of the Sennheiser EW300 units each with 2 body backs which I run in mono.
I have them next to each other in a rack with the antennas to the front and I have had zero problems and love them.
 I have the chance to purchase one more with one pack used but new condition and was wondering whether if I decide to add one more system if I need to think about getting one of those antenna combiner / distributer thingies. Is it really necessary at this point and in fact why would it be necessary at all? ... Benefits etc....
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jasonfinnigan

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Re: IEM distribution antenna / combiner
« Reply #1 on: June 14, 2014, 08:51:30 pm »

Just wondering about these .....
I have 2 of the Sennheiser EW300 units each with 2 body backs which I run in mono.
I have them next to each other in a rack with the antennas to the front and I have had zero problems and love them.
 I have the chance to purchase one more with one pack used but new condition and was wondering whether if I decide to add one more system if I need to think about getting one of those antenna combiner / distributer thingies. Is it really necessary at this point and in fact why would it be necessary at all? ... Benefits etc....

It would certainly be a good. I've always ran with them. Not only does it give you the option of using amplified antennas/paddles with a higher db gain but also keeps clutter down and looks nice. But for the real reason research more about Intermodulation. Basically it puts all the signal through a single source and makes them play nicer with each other and puts them out of a single (set) of antenna which are Biased only to the overall frequency of the operating abilities of the system. keep in mind if you are using the paddle antenna it should be vertical as the antenna on the bodypacks are as well, due to RF alignment it will give you better signals. (by a lot sometimes, I used to align AirFiber type systems off of cell towers and in increases signal quality greatly.)

http://en.wikipedia.org/wiki/Intermodulation
« Last Edit: June 14, 2014, 08:56:18 pm by JasonFinnigan »
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Lyle Williams

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Re: IEM distribution antenna / combiner
« Reply #2 on: June 15, 2014, 12:39:11 am »

It would certainly be a good. I've always ran with them. Not only does it give you the option of using amplified antennas/paddles with a higher db gain but also keeps clutter down and looks nice. But for the real reason research more about Intermodulation. Basically it puts all the signal through a single source and makes them play nicer with each other and puts them out of a single (set) of antenna which are Biased only to the overall frequency of the operating abilities of the system. keep in mind if you are using the paddle antenna it should be vertical as the antenna on the bodypacks are as well, due to RF alignment it will give you better signals. (by a lot sometimes, I used to align AirFiber type systems off of cell towers and in increases signal quality greatly.)

http://en.wikipedia.org/wiki/Intermodulation

Combined antennas are useful and practical, especially if you need to run cables a distance to an expensive antenna.  Some of the antenna splitters also allow you to power gear via the coax, eliminating a bit more clutter.

I don't buy the lower intermod argument.
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Keith Broughton

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Re: IEM distribution antenna / combiner
« Reply #3 on: June 15, 2014, 06:28:44 am »

Just wondering about these .....
I have 2 of the Sennheiser EW300 units each with 2 body backs which I run in mono.

This sounds like an IEM system so the use of "amplified antennas" is not possible.
Running 3 transmitters with their own antennas will work OK.
Combining transmitters to one antenna will allow you to have a choice of what type of antenna you need to use and be able to position it for best results.

You can probably find a used combiner at a good price if you are patient.
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Lyle Williams

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Re: IEM distribution antenna / combiner
« Reply #4 on: June 15, 2014, 06:40:31 am »

In the past Sennheiser rebranded Mini-Circuits ZAPD-21 splitter/combiners.  They are rated at up to 10w tx power.  Mini-Circuits is a RF component supplier to industry/labs/govts/etc.

I got mine as non-Sennheiser-branded new-old-stock from ebay.  I think they shipped from Israel.  They had SMA connectors so I needed to get SMA-to BNC cables.  All up less that $100 for a pair of splitters plus six cables.
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Jason Glass

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Re: IEM distribution antenna / combiner
« Reply #5 on: June 15, 2014, 10:36:49 pm »

In the past Sennheiser rebranded Mini-Circuits ZAPD-21 splitter/combiners.  They are rated at up to 10w tx power.  Mini-Circuits is a RF component supplier to industry/labs/govts/etc.

I got mine as non-Sennheiser-branded new-old-stock from ebay.  I think they shipped from Israel.  They had SMA connectors so I needed to get SMA-to BNC cables.  All up less that $100 for a pair of splitters plus six cables.

Hi Lyle,

Passive combiners are very useful, and the Mini-Circuits ZAPD line is excellent.  However, you must be sure that their inherent loss of 3dB per pair of combines, minus insertion loss, minus cable loss, plus antenna gain, will work within your link budget.  Considering that EW300 have a maximum RF output of 30mW, a 3-way passive combiner (4.5 dB loss minus .5 dB insertion loss) will drop to 9.486mW before cable loss.  This will often work fine with a good 25' low-loss cable, a well-tuned antenna, and a low noise environment, maybe out to around 75 feet from TX antenna to RX in direct line-of-sight.  As soon as you start kicking on lighting instruments, video walls & floors, computers, and all the other things at a gig that emit low-level RF, things can get hairy real fast.

I don't buy the lower intermod argument.

Too bad; you're missing out on the scientifically proven and longtime industrial track record of the isolators, circulators, and high-isolation components found in most decent active IEM combiners.  Using a spectrum analyzer, I have seen 3rd order IEM intermod peaks go from 15dB above the noise floor to undetectable below the noise floor after integrating an appropriate active combiner into the system.

When you use a Sennheiser AC-3 combiner, you get unity RF gain (or more) with extremely low noise and measurably lower power intermodulation products emitted.
« Last Edit: June 15, 2014, 10:58:10 pm by Jason Glass »
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jasonfinnigan

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Re: IEM distribution antenna / combiner
« Reply #6 on: June 15, 2014, 11:10:35 pm »

Hi Lyle,

Passive combiners are very useful, and the Mini-Circuits ZAPD line is excellent.  However, you must be sure that their inherent loss of 3dB per pair of combines, minus insertion loss, minus cable loss, plus antenna gain, will work within your link budget.  Considering that EW300 have a maximum RF output of 30mW, a 3-way passive combiner (4.5 dB loss minus .5 dB insertion loss) will drop to 9.486mW before cable loss.  This will often work fine with a good 25' low-loss cable, a well-tuned antenna, and a low noise environment, maybe out to around 75 feet from TX antenna to RX in direct line-of-sight.  As soon as you start kicking on lighting instruments, video walls & floors, computers, and all the other things at a gig that emit low-level RF, things can get hairy real fast.

Too bad; you're missing out on the scientifically proven and longtime industrial track record of the isolators, circulators, and high-isolation components found in most decent active IEM combiners.  Using a spectrum analyzer, I have seen 3rd order IEM intermod peaks go from 15dB above the noise floor to undetectable below the noise floor after integrating an appropriate active combiner into the system.

When you use a Sennheiser AC-3 combiner, you get unity RF gain (or more) with extremely low noise and measurably lower power intermodulation products emitted.

+1 Exactly.

Also another thing to keep in mind if you were to buy an active third party combiner; You have to really know what you are doing. The circuity in these tend to be biased to certain frequencies which may not be compatible with your wireless system.

A passive combiner may work but I would never use it on a stage where I planned on using high gain antenna's. A passive unit is really just a gloried BNC T connections (think of it like the coaxial cable splitter for your house)
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Lyle Williams

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Re: IEM distribution antenna / combiner
« Reply #7 on: June 16, 2014, 06:02:07 am »

+1 Exactly.

Also another thing to keep in mind if you were to buy an active third party combiner; You have to really know what you are doing. The circuity in these tend to be biased to certain frequencies which may not be compatible with your wireless system.

A passive combiner may work but I would never use it on a stage where I planned on using high gain antenna's. A passive unit is really just a gloried BNC T connections (think of it like the coaxial cable splitter for your house)

A passive combiner ensures that each transmitter sees the expected impedance.  That is not the case with a BNC T. 

Yes, splitters and coax cause signal loss.  The game we are playing here is to try and get a better signal-to-noise ratio by getting antennas with better directivity close to the IEM receivers.  We hope the coax loss is less than the loss caused by having our transmitter antennas stuck in a rack case behind some other crud.  That loss could be 30dB.  We put up with the splitter loss because we don't want to buy (or physically can't install) more antennas and coax runs.

Intermodulation products are created at frequencies related to the original frequencies.  Frequencies can be selected to cause the minimum harm to your own systems (ensuring that intermod products don't land on your other RX frequencies.  Intermod products are created when non-linear circuit elements are exposed to multiple signals.  Every 1dB increase in the original signals encountering the nonlinearity results in a 3B increase in the level of the intermod products.  Thinking about the previous sentence, pushing multiple signals down the one cable/antenna is not going to reduce intermod.  That said, I don't think intermod is a significant issue to users of handfuls of transmitters tuned to mic vendors channel plans.
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Lyle Williams

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Re: IEM distribution antenna / combiner
« Reply #8 on: June 16, 2014, 06:09:22 am »

I will accept that there are better and worse ways of combining signals into a single cable/antenna.  What I took issue with was (a possibly incorrect assumption on my part) the idea that multiple transmitters on one antenna was inherently better intermod-wise than individual antennas.
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Rob Spence

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Re: IEM distribution antenna / combiner
« Reply #9 on: June 16, 2014, 08:30:55 am »

One of the guys from a Shure has given a great presentation a number of times on intermod. He has a spectrum analyzer and proceeds to move a couple of belt packs closer together, then with three. Looking at the spectrum analyzer you can see the intermod products.

He shows that if you pick channels at random, you may get problems. Also, if you use the tools provided by the manufacturer (wireless workbench in this case), you will get channels that are not going to put intermod products on top of other active frequencies.


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Re: IEM distribution antenna / combiner
« Reply #9 on: June 16, 2014, 08:30:55 am »


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