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Author Topic: IEM combining best practices  (Read 3398 times)

Diogo Nunes Pereira

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IEM combining best practices
« on: June 03, 2017, 06:49:51 pm »

Since my original post was eaten by the internet while the forum was down, here it is again...

Hi,

I was wondering what is the best practice when active combining IEMs with fewer transmitters than combiner inputs. The situation I came about had me combining ten Shure PSM1000 transmitters into two Shure PA821 combiners. So I had 10 transmitters for a total of 16 available inputs.

I passive combined both active combiner outputs to spit all 10 frequencies thru the same antenna, but I questioned:

 - should I combine 8 transmitters in combiner A + 2 in combiner B?
 - should I use 5 inputs in each combiner?
 - If using only 2 inputs in combiner B, should I use inputs 1+2 or would 1+8 would provide better isolation?...
 - any other input arrangements?
 - should the free inputs have dummy loads?

I used same power settings for all transmitters and ended up combining 8+2, but these questions are still roaming my head.

Cheers,

d
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Diogo Nunes Pereira
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Neil White

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Re: IEM combining best practices
« Reply #1 on: June 04, 2017, 05:35:43 am »

Hi,

I was wondering what is the best practice when active combining IEMs with fewer transmitters than combiner inputs. The situation I came about had me combining ten Shure PSM1000 transmitters into two Shure PA821 combiners. So I had 10 transmitters for a total of 16 available inputs.

Hi Diogo,

I know the RAD TX-8 combiner makes specific mention about port to port isolation in its user guide HERE but I don't know if that is specific to the TX8  or general best practise for combiners.

Hopefully Henry will see this and give us the benefit of his knowledge on these units.

Neil
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Jean-Pierre Coetzee

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Re: IEM combining best practices
« Reply #2 on: June 04, 2017, 06:42:14 am »

Use 5 of each and put terminators on the remaining ports, don't leave the ports unterminated, that would be the biggest cause of issues.
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Diogo Nunes Pereira

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Re: IEM combining best practices
« Reply #3 on: June 05, 2017, 03:12:09 pm »



I know the RAD TX-8 combiner makes specific mention about port to port isolation in its user guide HERE but I don't know if that is specific to the TX8  or general best practise for combiners.

Hopefully Henry will see this and give us the benefit of his knowledge on these units.

Neil

Thanks Neil. It was actually this manual that made think about isolation issues in combiners. Isolation is something I'm still beginning to grasp.

Enviado desde mi XT1072 mediante Tapatalk

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Diogo Nunes Pereira
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Diogo Nunes Pereira

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Re: IEM combining best practices
« Reply #4 on: June 05, 2017, 03:18:59 pm »

Use 5 of each and put terminators on the remaining ports, don't leave the ports unterminated, that would be the biggest cause of issues.
This being such an issue I wonder why no combiner manual I've read so far mentioned it. Also why not sell the units with terminators for each port.

Is this also best practice for open splitter outputs?

Enviado desde mi XT1072 mediante Tapatalk

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Diogo Nunes Pereira
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Jean-Pierre Coetzee

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Re: IEM combining best practices
« Reply #5 on: June 05, 2017, 03:23:49 pm »

You should also terminate unused splitter ports.

Terminators cost nothing buy them and use them it doesn't hurt anyone
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Scott Helmke

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Re: IEM combining best practices
« Reply #6 on: June 05, 2017, 05:13:37 pm »

This being such an issue I wonder why no combiner manual I've read so far mentioned it. Also why not sell the units with terminators for each port.

Is this also best practice for open splitter outputs?

Year ago we had a Sony mic system where you were supposed to terminate the unused outputs on the antenna splitters.
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Henry Cohen

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Re: IEM combining best practices
« Reply #7 on: June 08, 2017, 06:18:01 pm »

This being such an issue I wonder why no combiner manual I've read so far mentioned it. Also why not sell the units with terminators for each port.

Is this also best practice for open splitter outputs?

All active combiners or splitters as sold for low power transmit and receive applications are based on the Wilkinson circuit, with circuits cascaded to achieve more inputs or outputs. The key benefit of this circuit is a relatively high isolation between the two individual ports, but with a minimal insertion loss between either individual port and the summed port. Although the Wilkinson circuit can be designed with individual port counts that are not 2^x, the simplest designs are in fact 2, 4, 8, 16 way, etc. Ports are simply cascaded.



So taking the port pairs at the opposite ends of the overall cascaded circuit will provide the greatest isolation.

Regarding the termination of unused ports, it's always a good practice, more so with receive multicouplers (splitters) to ensure proper impedance matching at each output port so as to minimize any reflected energy back into the circuit.

With TX combiners, it's not as crucial because each input goes directly to an amplifier stage which has a directivity spec; basically a reverse gain value (usually in the -20 to -30dB range), so reflected energy is rarely an issue. If there is a partial internal fault however, the termination on the input port can substantially reduce any oscillating reflections getting magnified in the amplifier stage.

"Also why not sell the units with terminators for each port?" Because the manufacturer has no idea how many ports you'll wan to use. Just buy them for your work kit. (Don't buy cheap no-name ones; their return loss is usually awful.)
« Last Edit: June 08, 2017, 06:20:16 pm by Henry Cohen »
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Henry Cohen

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Re: IEM combining best practices
« Reply #7 on: June 08, 2017, 06:18:01 pm »


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