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Title: IEM distribution antenna / combiner
Post by: Debbie Dunkley 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....
Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan 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
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams 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.
Title: Re: IEM distribution antenna / combiner
Post by: Keith Broughton 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.
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams 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.
Title: Re: IEM distribution antenna / combiner
Post by: Jason Glass 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.
Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan 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)
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams 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.
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams 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.
Title: Re: IEM distribution antenna / combiner
Post by: Rob Spence 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.


Sent from my iPad using Tapatalk HD
Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan on June 16, 2014, 09:30:52 pm
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.


Sent from my iPad using Tapatalk HD
I think I've seen that demo before.

But from experience I can tell you that intermod is a big issue from when I worked on cell towers dealing with both Point 2 point Wifi (site to site Air Fiber connections) and emergency services signals. There's a reason they make multiplexers.
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams on June 17, 2014, 06:17:32 am
Ok, I did some calculations and the intermod performance of a properly combined single antenna IS better than separate antennas, given the way sound people are likely to deploy those antennas.  Ie, close together and without crossed polarisation.

Rough calculations here on intermod product strength from two 30mW signals for B-band gear I have here seem to be about 1uW with the ZAPD-21 as a passive combiner.  Separate antennas yield worse performance until you get about 5m antenna separation.  A BNC-T is simply dreadful, maybe 100x worse than the passive combiner.

A circulator will be better than the ZAPD-21, but not hugely better.  Maybe 6-10dB?

How much do we care about a millionth of a watt interference as long as it is out-of-band relative to our gear?

(But I stand corrected.   :-)   )
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 17, 2014, 11:53:44 am
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....

Deb.. this thread got real technical, real quick.
FWIW - We have 4 PSM units and a Carvin EM900 in the rack with no intermod (so far) - all with front mount antennas, located on stage as band does not have FOH person.

We did look at the extra expense of antenna combination options, talked to a few folks who [basically] concluded that over the range in question, being stage located, not being mixed/xmitted from FOH, that we should NOT need the extra equipment expense. So far that has been proven to be correct.
YMMV.
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley on June 17, 2014, 11:58:29 am
Wow…thanks everyone - "be careful what you wish for"..
I understood only a small part of what has been discussed here - you peeps are all way too clever with this stuff!!!
Anyway, am I right in saying that adding one more unit to the 2 I already have wouldn't bring any problems for the most part?
The guy didn't get back to me on the Sennheiser EW300 I was looking at so I won't be adding another system just yet but when one comes up at the right price I'll probably give it a go without the antenna distributor and if I get problems, I'll just have to add one !!!.
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley on June 17, 2014, 12:01:50 pm
Deb.. this thread got real technical, real quick.
FWIW - We have 4 PSM units and a Carvin EM900 in the rack with no intermod (so far) - all with front mount antennas, located on stage as band does not have FOH person.

We did look at the extra expense of antenna combination options, talked to a few folks who [basically] concluded that over the range in question, being stage located, not being mixed/xmitted from FOH, that we should need the extra equipment expense. So far that has been proven to be correct.
YMMV.

Thanks Steve…ironically I just posted my comment as yours was posting too. I did get rather overwhelmed with the info being provided but I respect everyones knowledge and experience here  so I never want to sound unappreciative.

Good to know you are not having issues going this route...
Title: Re: IEM distribution antenna / combiner
Post by: Keith Broughton on June 17, 2014, 02:11:38 pm
To clarify, and simplify...
 "antenna combiner" takes multiple outputs from IEM transmitters and combines them to transmit on one antenna.
"Antenna distribution" takes one receive antenna and distributes it to multiple receivers.
You can use a "powered" (receive) antenna on a distribution system but only a "passive" (transmitter) antenna can be used on a combiner
Hope this helps :)
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 17, 2014, 04:07:44 pm
Thanks Steve…ironically I just posted my comment as yours was posting too. I did get rather overwhelmed with the info being provided but I respect everyones knowledge and experience here  so I never want to sound unappreciative.

Good to know you are not having issues going this route...

Yeah.. the guys on this forum are great! !!  Very knowledgeable and very helpful.. and some of them have more than helped me at times... I don't do the SR thing much anymore and have gone to the other side of the stage, but still try to stay "up" on things and try to apply what I've learned to current band.

Much as I actively prefer someone at FOH, reality is a number of the venues we play (35%?) have house systems and of the rest, many require that you mix from side of stage as they don't want console/wires out front.
Title: Re: IEM distribution antenna / combiner
Post by: Rob Spence on June 17, 2014, 11:42:26 pm
Ok, I did some calculations and the intermod performance of a properly combined single antenna IS better than separate antennas, given the way sound people are likely to deploy those antennas.  Ie, close together and without crossed polarisation.

Rough calculations here on intermod product strength from two 30mW signals for B-band gear I have here seem to be about 1uW with the ZAPD-21 as a passive combiner.  Separate antennas yield worse performance until you get about 5m antenna separation.  A BNC-T is simply dreadful, maybe 100x worse than the passive combiner.

A circulator will be better than the ZAPD-21, but not hugely better.  Maybe 6-10dB?

How much do we care about a millionth of a watt interference as long as it is out-of-band relative to our gear?

(But I stand corrected.   :-)   )

Last I checked, 6-10dB is a big deal.

Debby, are you using a tool to determine your frequencies? If so, be sure to include wireless mics as well.

Sent from my iPad using Tapatalk HD
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams on June 18, 2014, 02:39:33 am
Last I checked, 6-10dB is a big deal.

To clarify, the offending intermod signal (which should fall on a frequency that you are not using) would be about 50dB down in strength from your main signal if using the passive combiner.  Using a circulator/duplexor might mean that the offending signal might be 56-60dB down in strength from your main signal.

Even if it was zero dB down, it would cause you no problems unless it fell on another frequency you are using!  If you stick to vendor recommended intermod-free channel allocations you should largely be immune from self-generated intermod problems.

This is nothing to do with the quality of the audio.  This is just to do with how much RF garbage you leave around for others who may use the RF spectrum.  As wireless mics are a secondary user of spectrum, you should worry (or not worry!) about the interference caused by your main signal before you worry (or not) about your intermod products.  :-)

(RF-wise, this issue is about as big a deal as two people with mobile phones sitting next to each other on a bus....)
Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan on June 18, 2014, 03:12:24 pm

(RF-wise, this issue is about as big a deal as two people with mobile phones sitting next to each other on a bus....)

I don't care to go into all the details now but, this isn't the same thing at all.
Title: Re: IEM distribution antenna / combiner
Post by: Mac Kerr on June 18, 2014, 04:25:16 pm
Even if it was zero dB down, it would cause you no problems unless it fell on another frequency you are using!  If you stick to vendor recommended intermod-free channel allocations you should largely be immune from self-generated intermod problems.

While this is true, it ignores the fact that the manufacturers groups only work within that group, you cannot combine groups, nor can you combine systems from different manufacturers, including any RF comm that may be in the UHF band. The manufacturers groups are limited in the number of RF mics you can use, and AFAIK don't include any IEMs. They also do not take any DTV in the area into consideration.

Using good IM software like WWB, or IAS will let you freely choose compatible for all your systems, allowing a far greater number of mics, as well as IEM and RF comms. While it is best to do an on site RF scan with a spectrum analyzer, all the major IM software systems will block out any DTV in the FCC database.

Once you have moved on to using one of the (often free) IM programs you are no longer limited to the few channels in the manufacturers groups.

Mac
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams on June 19, 2014, 05:27:55 am
I agree that if you are bringing a whole rack of wireless gear then you should plan ahead.

Many low scale users of wireless products get by just fine without knowing any more than "set each unit to a different frequency".
Title: Re: IEM distribution antenna / combiner
Post by: Jordan Wolf on June 19, 2014, 09:15:15 am
Debbie,

Sennheiser has a free software program (for Windows (http://javascript:%20open_downloadFile%20('Sennheiser_WSM_Setup_4_1_24_XPWin78.exe','2586D470A683D31EC1257CE0002B7E86','1','');) or Mac (http://javascript:%20open_downloadFile%20('Sennheiser_WSM_Setup_4_1_24_MAC.dmg','2586D470A683D31EC1257CE0002B7E86','1','');)) that will allow you to input your various devices and calculate frequencies for them based on the number of units, bandwidth occupied, etc.  If your units have the ability to network together, you may even be able to scan the local RF environment to further refine the frequencies that are available to you.

NorthernSound has a walkthrough video (http://) of the program and here's the official user guide (http://94.100.244.130/sennheiser/sw-downloads.nsf/resources/WSM_A01_0513_EN_INT.pdf/$File/WSM_A01_0513_EN_INT.pdf).

It would be good to get friendly with this software, and I think you'll find that you'll have more peace-of-mind at events when you know you've done as much as you could to ensure good wireless coordination for your gear.
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley on June 19, 2014, 11:08:50 am
Last I checked, 6-10dB is a big deal.

Debby, are you using a tool to determine your frequencies? If so, be sure to include wireless mics as well.

Sent from my iPad using Tapatalk HD

Hi Rob…no I am not using any measuring tools of any kind.
I am quite new to the wireless thing really.
Years ago when I was singing I used one of the early Nady Mics (there wasn't much choice back then) and it was such a horrible experience,  I immediately went back to wired till the very last gig I sang a few years ago. IEM's were unheard of for most of my career and to be honest, I never even used wedge monitors for the first few years back then…."The kids of today don't know they've got it made" ….  anyway- I digress….. 
For the most part this is a recent transition to the world of wireless  for me. Hubby has a wireless mic which we have not yet used WITH the iems on stage yet. I was just trying to be prepared for any issues that may arise. So far I have had none with the iems running them with separate antennas. Bear in mind right now I have 2 systems (2 transmitters, 4 receivers).
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley on June 19, 2014, 04:14:36 pm
Debbie,

Sennheiser has a free software program (for Windows (http://javascript:%20open_downloadFile%20('Sennheiser_WSM_Setup_4_1_24_XPWin78.exe','2586D470A683D31EC1257CE0002B7E86','1','');) or Mac (http://javascript:%20open_downloadFile%20('Sennheiser_WSM_Setup_4_1_24_MAC.dmg','2586D470A683D31EC1257CE0002B7E86','1','');)) that will allow you to input your various devices and calculate frequencies for them based on the number of units, bandwidth occupied, etc.  If your units have the ability to network together, you may even be able to scan the local RF environment to further refine the frequencies that are available to you.

NorthernSound has a walkthrough video (http://) of the program and here's the official user guide (http://94.100.244.130/sennheiser/sw-downloads.nsf/resources/WSM_A01_0513_EN_INT.pdf/$File/WSM_A01_0513_EN_INT.pdf).

It would be good to get friendly with this software, and I think you'll find that you'll have more peace-of-mind at events when you know you've done as much as you could to ensure good wireless coordination for your gear.

Thanks Jordan…
yes I think I need to do some research. I'd rather be prepared before and in case anything happens rather than be surprised if it does and unable to correct the problems……….don't like surprises like that!!!
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 19, 2014, 04:34:36 pm
Thanks Jordan…
yes I think I need to do some research. I'd rather be prepared before and in case anything happens rather than be surprised if it does and unable to correct the problems……….don't like surprises like that!!!

Deb, I don't pretend to be knowledgeably in the wireless area at all, but I'd GUESS you will NOT have any of the issue outlined in this thread unless you run MANY/multiple sets of wireless devices.

We have the following at a gig (tomorrow night is next gig) and not a lick of interference/crosstalk - I assume - because they are configured to all run on separate channels/bands:
1 wireless mic on lead vox
1 wireless acoustic gtr (G50)
2 wireless electrics  (G50's)
1 wireless bass (G90)
5 IEM devices.. (4*PSM200, 1*EM900).

That's 10 devices on stage with no issues.. I don't know where the boundaries are and I'm not saying it couldn't or wouldn't ever happen, but based on my limited exposure and impression(s) from talking with local folks "in the know", you need some level of scale to occur. Is that 12 devices, 20? idk.

We could get concerned, but we're not going to worry about it for now. We're also not likely to have any stadium gigs in the next week or 2 :)
Title: Re: IEM distribution antenna / combiner
Post by: Tim McCulloch on June 19, 2014, 04:52:44 pm
Steve, the problems begin when the 2nd transmitter is turned on.  Just because you're not *obviously* stepping on your own signals doesn't mean that you're not creating problems.
Title: Re: IEM distribution antenna / combiner
Post by: Mac Kerr on June 19, 2014, 04:58:40 pm
Deb, I don't pretend to be knowledgeably in the wireless area at all, but I'd GUESS you will NOT have any of the issue outlined in this thread unless you run MANY/multiple sets of wireless devices.

We have the following at a gig (tomorrow night is next gig) and not a lick of interference/crosstalk - I assume - because they are configured to all run on separate channels/bands:
1 wireless mic on lead vox
1 wireless acoustic gtr (G50)
2 wireless electrics  (G50's)
1 wireless bass (G90)
5 IEM devices.. (4*PSM200, 1*EM900).

That's 10 devices on stage with no issues.. I don't know where the boundaries are and I'm not saying it couldn't or wouldn't ever happen, but based on my limited exposure and impression(s) from talking with local folks "in the know", you need some level of scale to occur. Is that 12 devices, 20? idk.

We could get concerned, but we're not going to worry about it for now. We're also not likely to have any stadium gigs in the next week or 2 :)

Any time you run 3 or more wireless devices you run the risk of interference from intermodulation products. There are at least 2 FREE RF management programs, one from Shure, one from Sennheiser. Either one will work with Shure, Sennheiser, or Lectrosonics products. There is no excuse for not taking this simple step to help assure that you are not causing interference with your own system. There is not a point at which IM suddenly becomes a problem other than the minimum of 3 systems. Every combination of 2 or more RF transmitters causes IM products, but with only 2 they won't interfere with each other. As soon as you add more than 2 you open the possibility that one of those IM products will fall on one of your active frequencies.

The software is fairly easy to use, and can be run in advance. If you enter the ZIP code of the venue the software will look up TV stations in the area and include them in any calculations.

While it is better to have a recent scan of the RF in the venue, a combination of asking what other RF is in use, and the data the software looks up online will give you a better chance than you have now of success.

If you are running IEMs and mics you should try to keep the IEM frequencies separated from the mics as much as possible.

Mac
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 19, 2014, 05:22:55 pm

thanks Mac.. I wasn't aware of that.. will take the recommendations and see what we end up with..    Like I said above... wonderful folks on this board !

One question... ??   I'm sure Deb is interested too..
Is it necessary to "profile" and adjust settings for each venue - assuming local radio/tv interference intensity will likely vary ?
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 19, 2014, 05:24:31 pm
Steve, the problems begin when the 2nd transmitter is turned on.  Just because you're not *obviously* stepping on your own signals doesn't mean that you're not creating problems.

thanks Tim.. I'm assuming that we have enough separation with the the devices that nothing has reared it's ugly head yet...  I'm going to take Mac's advice and run the test on the band's gear and make sure it doesn't happen to us..
Title: Re: IEM distribution antenna / combiner
Post by: Lyle Williams 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.

Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge 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 :)
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley 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…  :-\
Title: Re: IEM distribution antenna / combiner
Post by: Pete Erskine 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 (http://www.tti-test.com/go/psa/tour2-0-topics.htm) 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 (http://www.bestaudio.com/Freq_coord.htm).  The RF Coordination for Roadies manual might answer a lot of your questions
Title: Re: IEM distribution antenna / combiner
Post by: Jerome Malsack 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. 
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley 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.
Title: Re: IEM distribution antenna / combiner
Post by: Pete Erskine 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 (http://www.bestaudio.com/_private/downloads/channels.zip)
Title: Re: IEM distribution antenna / combiner
Post by: Jerome Malsack on June 20, 2014, 01:01:07 pm
http://en.wikipedia.org/wiki/North_American_television_frequencies
Title: Re: IEM distribution antenna / combiner
Post by: brian maddox 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....
Title: Re: IEM distribution antenna / combiner
Post by: Debbie Dunkley 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???
Title: Re: IEM distribution antenna / combiner
Post by: Jerome Malsack on June 20, 2014, 01:43:58 pm
You are doing very well.  The problem is how many watts of power those TV stations put out and your little transmitters are competing for the radio space.   If you get to close, the TV station will be all you can hear.  The mic will not over power the TV transmitter.  Loudest at the antenna wins. 

Yes a pun on the   loudest at the mic    Feedback.   

Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan on June 20, 2014, 02:44:59 pm
Just thought I will through this in here for any of the new people to RF. Espcially if you are buying used wireless gear check the frequencies. in the US the FCC has made many of those freely available before as now restricted channels. I'm not sure if what Shure gear does, but I know the Sennheiser G2 stuff has illegal frequencies is some of it, with G3 you should be safe.
Title: Re: IEM distribution antenna / combiner
Post by: brian maddox on June 20, 2014, 03:28:01 pm
Just thought I will through this in here for any of the new people to RF. Espcially if you are buying used wireless gear check the frequencies. in the US the FCC has made many of those freely available before as now restricted channels. I'm not sure if what Shure gear does, but I know the Sennheiser G2 stuff has illegal frequencies is some of it, with G3 you should be safe.

To clarify...

In the US it is now illegal to operate RF devices between 698 and 806 MHz [usually referred to as the '700 MHz band'].  There are many manufacturers that make units that operate in these frequencies, so when purchasing used equipment it is definitely buyer beware. 

To make things more complicated, every manufacturer uses their own set of Letter Codes to define their various frequency bands.  Shure's in particular is quite complicated with many overlapping bands for different areas of this country as well as international use.  Again, it is imperative that you do your homework when buying used equipment.

FWIW, Sennheiser Band C sits squarely in the forbidden zone.  As far as i know Band C is still available with G3 series stuff, although it would probably be less likely to appear in the US, as G3 was introduced close to the same time as the 700 MHz ban took effect.
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 23, 2014, 04:53:44 pm
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 (http://www.tti-test.com/go/psa/tour2-0-topics.htm) 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 (http://www.bestaudio.com/Freq_coord.htm).  The RF Coordination for Roadies manual might answer a lot of your questions

Pete,

thanks for the feedback.. went to your page and looked at the pdf there.. very informative. However, I would imagine that the cost to follow your process is cost prohibitive (or W-A-Y outside the budget) for the average weekend warrior types - tho' the spreadsheet was VERY informative.   Thanks for sharing that!

This weekend were were at a venue we've played many times before, but not since going all IEM's. We had 5 sets of IEM's running (4 * PSM200 and 1 * Carvin EM900), plus a combination of 4 * L6 G90/G50/G30's.   All devices are channel separated - as much as possible - on both input and output transmitters/receivers.

There was no intermod/cross-talk that we could discern. There was a little interference (that I observed while standing in one spot on the stage and turning slightly), but no-one else complained about it or brought it up.  This was typical sports-bar/club-level room with TV's going.

This has been our experience in other venues we play, but the overwhelming feedback posted here in response to Deb (and I ) is based on this being "an accident waiting to happen"  !!

OK. I can understand that, but can you/someone advise as to how to do this is a cost-effective manner ?  I've looked at Senn's WSM, Shure's WWB v6 ...  where does one find data for devices outside the inventory in those software packages.. eg: Line6, Carvin ?

Title: Re: IEM distribution antenna / combiner
Post by: jasonfinnigan on June 23, 2014, 05:23:02 pm

OK. I can understand that, but can you/someone advise as to how to do this is a cost-effective manner ?

Do research on what frequencies you are using and where the intermod is laying. Also selling off your wireless gear and standardizing on one solution would help make it simpler.


I've looked at Senn's WSM, Shure's WWB v6 ...  where does one find data for devices outside the inventory in those software packages.. eg: Line6, Carvin ?

I'm not sure about Shure as  I don't use theirs much. but in WSM you can add a device and configure every single frequency of it, so you can really input any device once you look up the specs for it from the manufacturer.
Title: Re: IEM distribution antenna / combiner
Post by: Steve Oldridge on June 24, 2014, 10:21:43 am
Do research on what frequencies you are using and where the intermod is laying. Also selling off your wireless gear and standardizing on one solution would help make it simpler.


I'm not sure about Shure as  I don't use theirs much. but in WSM you can add a device and configure every single frequency of it, so you can really input any device once you look up the specs for it from the manufacturer.

thanks Jason .. will go that route.