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Author Topic: IEM Antenna placement advice  (Read 4851 times)

Guy Morris

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IEM Antenna placement advice
« on: February 22, 2016, 11:55:32 am »

Hi

Some advice please from the RF gurus on the forum or any users in the same situation!

I'm looking for best practice here.

Scenario:  Rack 1  8x Sennheiser Radio mics and distribution amps
               Rack 2  12 x Sennheiser IEM in blocks of 4 with 3 Antenna combiners.(4 max
               TX units per combiner)

Set up:    Each rack is normallyseparated by 8ft distance (one either side of the desk)
              Radio Mic Rack has just 2x Directional RX Antenna for the 8 receivers
              IEM Rack has to have an TX Antenna for every 4 units so 3 x Antenna

Sennheiser suggested to me that the Radio mic antenna can be a few feet apart for best Diversity results but will work fine on a dual space bar on one stand (space saving and neat) and this seems to be the case with no issues.

What I am not sure about is if the IEM antennas could be set up the same way with the 3 of them mounted on 4 space bar on just one stand.

I am aware of always placing the IEM antenna in front of the Radio mic ones if space is limited  and ensuring that they don't point at each other (eg from either side of the stage).

They all have Sennheiser passive directional paddles and identical 50 ohm 5mtr coax.

The IEM systems will only allow 4 TX per combiner and no link through to another combiner (unlike the radio mic systems) so 3 antenna is what is required but what problems could be encountered if they are placed close to each other and if not a good idea what distance between each antenna is best (Sennheiser do not seem to offer any advice on this subject!)

Thanks

Guy

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Pete Erskine

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Re: IEM Antenna placement advice
« Reply #1 on: February 22, 2016, 12:06:52 pm »

I am aware of always placing the IEM antenna in front of the Radio mic ones if space is limited  and ensuring that they don't point at each other (eg from either side of the stage).

They all have Sennheiser passive directional paddles and identical 50 ohm 5mtr coax.

The IEM systems will only allow 4 TX per combiner and no link through to another combiner (unlike the radio mic systems) so 3 antenna is what is required but what problems could be encountered if they are placed close to each other and if not a good idea what distance between each antenna is best (Sennheiser do not seem to offer any advice on this subject!)

Personally I would put RX antenna in front if I couldn't separate them to the side.  Just like to get RX antennas as close to performer as possible - TX has more power so doesn't need less distance.  Probably not a big deal either way since the rear null for TX and RX are both probably good protection from each other. 

I would still have at least 6' spacing between TX and RX either side by side or front and Back..  I have never had any bad issues in placing all the TX antennas relatively close to each other (<2' each) as long as the strictest IM calculations have been done on the freqs.  That being said more clear space around a TX antenna makes for the best RF field to develop.
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Jason Glass

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Re: IEM Antenna placement advice
« Reply #2 on: February 22, 2016, 12:12:19 pm »

Hi

Some advice please from the RF gurus on the forum or any users in the same situation!

I'm looking for best practice here.

Scenario:  Rack 1  8x Sennheiser Radio mics and distribution amps
               Rack 2  12 x Sennheiser IEM in blocks of 4 with 3 Antenna combiners.(4 max
               TX units per combiner)

Set up:    Each rack is normallyseparated by 8ft distance (one either side of the desk)
              Radio Mic Rack has just 2x Directional RX Antenna for the 8 receivers
              IEM Rack has to have an TX Antenna for every 4 units so 3 x Antenna

Sennheiser suggested to me that the Radio mic antenna can be a few feet apart for best Diversity results but will work fine on a dual space bar on one stand (space saving and neat) and this seems to be the case with no issues.

What I am not sure about is if the IEM antennas could be set up the same way with the 3 of them mounted on 4 space bar on just one stand.

I am aware of always placing the IEM antenna in front of the Radio mic ones if space is limited  and ensuring that they don't point at each other (eg from either side of the stage).

They all have Sennheiser passive directional paddles and identical 50 ohm 5mtr coax.

The IEM systems will only allow 4 TX per combiner and no link through to another combiner (unlike the radio mic systems) so 3 antenna is what is required but what problems could be encountered if they are placed close to each other and if not a good idea what distance between each antenna is best (Sennheiser do not seem to offer any advice on this subject!)

Thanks

Guy

Best practice rules of thumb:

Receive antennas >1λ apart (approx. 24 inches @UHF) but as far apart as is practical, with coverage overlapping the performance area.  Placed in pattern nulls or behind any transmit antennas (IEM, Intercom, etc.)

Transmit antennas >10 feet from any receiving antennas, >5 feet away from other transmit antennas.

These rules can be bent, of course.  I have placed TX antennas as close as 3ft. to RX with high and/or low pass filters inserted to minimize crosstalk.

Henry Cohen

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Re: IEM Antenna placement advice
« Reply #3 on: February 22, 2016, 04:16:34 pm »

Best practice rules of thumb:

Receive antennas >1λ apart (approx. 24 inches @UHF) but as far apart as is practical, with coverage overlapping the performance area.  Placed in pattern nulls or behind any transmit antennas (IEM, Intercom, etc.)

Transmit antennas >10 feet from any receiving antennas, >5 feet away from other transmit antennas.

These rules can be bent, of course.  I have placed TX antennas as close as 3ft. to RX with high and/or low pass filters inserted to minimize crosstalk.

Don't forget vertical separation: RX antennas above head (and other obstruction) height, TX antennas a minimum of 3' above that. The greater your frequency separation (between mics and ears), the less critical is spatial separation. This is where filters help.

One other point to consider is passively combining the outputs of the three TX combiners so that you have only one TX antenna, IF your RF signal at the IEM receiver can accommodate the approximate 5dB splitter loss.
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Guy Morris

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Re: IEM Antenna placement advice
« Reply #4 on: February 23, 2016, 07:53:19 am »

Personally I would put RX antenna in front if I couldn't separate them to the side.  Just like to get RX antennas as close to performer as possible - TX has more power so doesn't need less distance.  Probably not a big deal either way since the rear null for TX and RX are both probably good protection from each other. 

I would still have at least 6' spacing between TX and RX either side by side or front and Back..  I have never had any bad issues in placing all the TX antennas relatively close to each other (<2' each) as long as the strictest IM calculations have been done on the freqs.  That being said more clear space around a TX antenna makes for the best RF field to develop.

I have just noticed that my post may have been misleading regarding spacing.(not between the TX and RX as such,all helpful answers however!)  it was more about how close could each TX antenna be to another one the initial thought being I could place all 3 on a 4 way mic spacing bar like this one:

http://www.bhphotovideo.com/c/product/195935-REG/K_M_23600_500_55_236_Four_Microphone.html

Reading the replies it suggests that it is not a good idea! with Jason suggesting no closer to each other that 5ft per TX antenna.(noted)
It certainly would be good just to have just one antenna but Sennheiser said no to using another 'master' active combiner and touched on the loss issue with a passive solution hence my query on best placement while trying not to have a forest of stands (looks like that will be the way it is!)

Thanks

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Keith Broughton

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Re: IEM Antenna placement advice
« Reply #5 on: February 23, 2016, 09:31:54 am »

Don't forget vertical separation: RX antennas above head (and other obstruction) height, TX antennas a minimum of 3' above that. The greater your frequency separation (between mics and ears), the less critical is spatial separation. This is where filters help.

One other point to consider is passively combining the outputs of the three TX combiners so that you have only one TX antenna, IF your RF signal at the IEM receiver can accommodate the approximate 5dB splitter loss.
Henry, you were very specific about the "passive" part of combining.
Are there inherent problems with active combiners such as Sennheiser AC3?
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Pete Erskine

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Re: IEM Antenna placement advice
« Reply #6 on: February 23, 2016, 10:04:45 am »

Henry, you were very specific about the "passive" part of combining.
Are there inherent problems with active combiners such as Sennheiser AC3?

You are already using combiners to make groups of 4.  Adding more amplifiers after would do irreparable damage to your spectrum with strong IM.  Passive does not do that.  Replace your 1x4 combiner with one with more inputs would lower your antenna count,

However dividing your IEM into several TX could be an advantage.  Maybe your headliner gets max power to cover far out on stage and the band lower since they are close.
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Jason Glass

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Re: IEM Antenna placement advice
« Reply #7 on: February 23, 2016, 10:43:21 am »

You are already using combiners to make groups of 4.  Adding more amplifiers after would do irreparable damage to your spectrum with strong IM.  Passive does not do that.  Replace your 1x4 combiner with one with more inputs would lower your antenna count,

However dividing your IEM into several TX could be an advantage.  Maybe your headliner gets max power to cover far out on stage and the band lower since they are close.

Pete's advice here is solid.  One issue to consider with Sennheiser EW/G3 IEM and combining is their relatively low maximum output power of 30mW (unless you have 2050's).  If you passively combine 3 ways, this output power is reduced to  9.4mW or less.  This is rather low, but might do the job OK depending on your range and coverage requirements, transmission line type and length, and transmitting antenna gain and pattern.

Keith Broughton

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Re: IEM Antenna placement advice
« Reply #8 on: February 23, 2016, 11:41:44 am »

You are already using combiners to make groups of 4.  Adding more amplifiers after would do irreparable damage to your spectrum with strong IM.  Passive does not do that.  Replace your 1x4 combiner with one with more inputs would lower your antenna count,

However dividing your IEM into several TX could be an advantage.  Maybe your headliner gets max power to cover far out on stage and the band lower since they are close.
Looks like I mis read the OP. Not reading all the info  :-[
Yes, I use a passive combiner to add the outputs of 2 AC3 units.
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Lyle Williams

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Re: IEM Antenna placement advice
« Reply #9 on: February 23, 2016, 12:54:00 pm »

When running linearly polarised diversity antennas think about polarisation diversity too.  Eg, if you have a pair of paddles, keep them both pointed at the stage but tip one 45 deg left and the other 45 deg right.

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Guy Morris

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Re: IEM Antenna placement advice
« Reply #10 on: March 21, 2016, 01:21:49 pm »

When running linearly polarised diversity antennas think about polarisation diversity too.  Eg, if you have a pair of paddles, keep them both pointed at the stage but tip one 45 deg left and the other 45 deg right.

Thank you everyone for your replies on this, some useful comments to consider.


Guy
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Re: IEM Antenna placement advice
« Reply #10 on: March 21, 2016, 01:21:49 pm »


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