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Author Topic: Combiner - Analog vs Digital  (Read 3188 times)

Mark Hannah

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Combiner - Analog vs Digital
« on: March 09, 2018, 09:36:34 am »

Hello all,

Multicouper usage with digitally modulated IEMs?

We are considering Lectrosonics' Duet system to replace our 600Mhz IEMs.  Lectrosonics is recommending Shure PA421/821B combiners.  We already own PWS GX-8s.

What are your thoughts about using digitally modulated gear with the currently available combiners?  How about using the combiner with both FM and digital at the same time?

I would appreciate a simple and something that gets into more detail (to help expand my knowledge).

Thank you.
« Last Edit: March 12, 2018, 08:58:23 am by Mark Hannah »
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Neil White

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Re: Multicouper - Analog vs Digital
« Reply #1 on: March 09, 2018, 12:36:08 pm »

We are considering Lectrosonics' Duet system to replace our 600Mhz IEMs.  Lectrosonics is recommending Shure PA421/821B combiners.  We already own PWS GX-8s.

I seem to recall reading something about the Automatic Gain Compensation in the GX-8 not playing nicely with digital carriers, but my google skills are coming up short. If thats the case the PA821 or RAD TX-8 shouldn't be affected as they are fixed or switchable gain.

I'm sure Henry or one of the PWS guys will be along to point us in the right direction shortly :)
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Henry Cohen

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Re: Multicouper - Analog vs Digital
« Reply #2 on: March 09, 2018, 04:39:09 pm »

Multicouper usage with digitally modulated IEMs?

We are considering Lectrosonics' Duet system to replace our 600Mhz IEMs.  Lectrosonics is recommending Shure PA421/821B combiners.  We already own PWS GX-8s.

What are your thoughts about using digitally modulated gear with the currently available combiners?  How about using the combiner with both FM and digital at the same time?

I would appreciate a simple and something that gets into more detail (to help expand my knowledge).

First, on a pedantic note, in the real world of RF, "multicoupler" refers to a receive path device that takes a single input from an antenna and splits to several outputs. "Combiner" is the correct term for combining multiple transmitters into one antenna.

On to the topic at hand . . . The GX8 will not work under any circumstances with digital transmission schemes. As Neil alluded to, the AGC circuit simply can not lock onto the wideband carrier and thus sends erroneous voltage levels to the control amp. It's also not nearly linear enough.

The Shure units will definitely work. Lectro is also finishing up testing on the RAD TX-8U; Maybe Karl can chime in on their findings but it worked for us. Do note however, it must be the latest hardware version with the "U" in the model name; earlier units will not work with the digital modulation.
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Henry Cohen

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Karl Winkler

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Re: Multicouper - Analog vs Digital
« Reply #3 on: March 09, 2018, 05:04:10 pm »

First, on a pedantic note, in the real world of RF, "multicoupler" refers to a receive path device that takes a single input from an antenna and splits to several outputs. "Combiner" is the correct term for combining multiple transmitters into one antenna.

On to the topic at hand . . . The GX8 will not work under any circumstances with digital transmission schemes. As Neil alluded to, the AGC circuit simply can not lock onto the wideband carrier and thus sends erroneous voltage levels to the control amp. It's also not nearly linear enough.

The Shure units will definitely work. Lectro is also finishing up testing on the RAD TX-8U; Maybe Karl can chime in on their findings but it worked for us. Do note however, it must be the latest hardware version with the "U" in the model name; earlier units will not work with the digital modulation.

We haven't had a chance to thoroughly test the latest RAD combiner, but we're hopeful it looks good because it has a nice set of features.
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Jason Glass

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Re: Multicouper - Analog vs Digital
« Reply #4 on: March 10, 2018, 02:59:43 pm »



Do note however, it must be the latest hardware version with the "U" in the model name; earlier units will not work with the digital modulation.

Thank you for the info, Henry. I was unaware of this HW update.

Sent from my Nexus 5 using Tapatalk

Mark Hannah

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Re: Combiner - Analog vs Digital
« Reply #5 on: March 12, 2018, 08:55:43 am »

First, on a pedantic note, in the real world of RF, "multicoupler" refers to a receive path device that takes a single input from an antenna and splits to several outputs. "Combiner" is the correct term for combining multiple transmitters into one antenna.

Henry,

Ah yes.  Quite confusing as I used both combiner and multicoupler in the same post...  Updated the Subject.

What about combining analog and digital in the same combiner?

We haven't had a chance to thoroughly test the latest RAD combiner, but we're hopeful it looks good because it has a nice set of features.

Karl,

Would you be willing to follow up on this post when Lectrosonics completes testing on the RAD combiner?

Thank you in advance.
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Henry Cohen

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Re: Combiner - Analog vs Digital
« Reply #6 on: March 12, 2018, 09:51:46 pm »

What about combining analog and digital in the same combiner?

Should not be a problem. Just adhere to proper frequency spacing requirements as per device.
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Henry Cohen

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Karl Winkler

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Re: Combiner - Analog vs Digital
« Reply #7 on: March 26, 2018, 04:12:51 pm »

Henry,

Ah yes.  Quite confusing as I used both combiner and multicoupler in the same post...  Updated the Subject.

What about combining analog and digital in the same combiner?

Karl,

Would you be willing to follow up on this post when Lectrosonics completes testing on the RAD combiner?

Thank you in advance.

Yes - I'll be happy to do so.
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Karl Winkler

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Re: Combiner - Analog vs Digital
« Reply #8 on: April 05, 2018, 05:06:48 pm »


Karl,

Would you be willing to follow up on this post when Lectrosonics completes testing on the RAD combiner?

Thank you in advance.

Hi Mark,

OK, we have our report back from engineering on the TX-8U combiner from RAD:

"This unit seems to be satisfactory for use with our digital and analog systems. Testing was performed using both our 50mW digital systems (Dba/DR - similar to M2 in terms of modulation) and our 250mW IFB system (IFBT4/IFBR1A). IMD performance was good in the TV broadcast band. Here we see 4 carriers applied to inputs 1-4. No degradation of the input signals was noticed, and the walk testing revealed no impairment of system performance."

-Karl
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Henry Cohen

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Re: Combiner - Analog vs Digital
« Reply #9 on: April 06, 2018, 10:34:11 pm »

OK, we have our report back from engineering on the TX-8U combiner from RAD:

"This unit seems to be satisfactory for use with our digital and analog systems. Testing was performed using both our 50mW digital systems (Dba/DR - similar to M2 in terms of modulation) and our 250mW IFB system (IFBT4/IFBR1A). IMD performance was good in the TV broadcast band. Here we see 4 carriers applied to inputs 1-4. No degradation of the input signals was noticed, and the walk testing revealed no impairment of system performance."

-Karl

[RAD hat on]

Thank you Karl. I would like to clarify some suggested settings for users:

- 50-60mW CW is the recommended input level into the TX-8U. This means using a 6dB attenuator on the output of the IFBT-4 (or T-1). It also means you may have to set the Duet power output to 25mW as its broader band spectral mask is more composite power than that of an analog CW carrier.

- The output of the TX-8 can be set to 250mW for an IFBT-x but probably should not be set higher than 100mW for the Duet.

- At minimum, follow standard practice for channel spacing, but adding another 50% or so (spectrum permitting) is advisable for the higher output TX-8U power settings.

[/RAD hat off]
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Henry Cohen

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