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Author Topic: BTR 800 antenna combining  (Read 4365 times)

Keith Broughton

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BTR 800 antenna combining
« on: September 16, 2016, 02:01:45 pm »

I have 2 BTR 800 units in the same E88 range.
The idea is to use a passive combiner to allow for the TX outs to couple to 1 TX antenna and a separate passive splitter for 1 receive antenna to split to each receiver.
Thinking of the Shure UA221 and 6 db omni antennas of the appropriate frequency range.

Thoughts?
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Pete Erskine

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Re: BTR 800 antenna combining
« Reply #1 on: September 16, 2016, 02:31:14 pm »

I have 2 BTR 800 units in the same E88 range.
The idea is to use a passive combiner to allow for the TX outs to couple to 1 TX antenna and a separate passive splitter for 1 receive antenna to split to each receiver.
Thinking of the Shure UA221 and 6 db omni antennas of the appropriate frequency range.

Thoughts?

Rx is not a problem.  You might experience excessive intermod combining the "already combined internally" TX frequencies with another Base.  Won't hurt but you might need to fiddle with freqs and might affect other wireless.

Correct way is to bypass the internal combiner and bring out each TX frequency separately and then use a proper isolated TX combiner such as the Rad TX-1 or Shure PA821.

See the paper on combining BTR on my website downloads page.  http://www.bestaudio.com/s/BTR_antenna_extend_coverage.pdf
« Last Edit: September 16, 2016, 02:33:27 pm by Pete Erskine »
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Keith Broughton

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Re: BTR 800 antenna combining
« Reply #2 on: September 16, 2016, 03:47:45 pm »

Rx is not a problem.  You might experience excessive intermod combining the "already combined internally" TX frequencies with another Base.  Won't hurt but you might need to fiddle with freqs and might affect other wireless.

Correct way is to bypass the internal combiner and bring out each TX frequency separately and then use a proper isolated TX combiner such as the Rad TX-1 or Shure PA821.

See the paper on combining BTR on my website downloads page.  http://www.bestaudio.com/s/BTR_antenna_extend_coverage.pdf
Kind of thought that might be the case so I would use separate TX antennas as it would be easier and cost effective.
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Diogo Nunes Pereira

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Re: BTR 800 antenna combining
« Reply #3 on: September 16, 2016, 04:31:36 pm »

Rx is not a problem.  You might experience excessive intermod combining the "already combined internally" TX frequencies with another Base.  Won't hurt but you might need to fiddle with freqs and might affect other wireless.

Correct way is to bypass the internal combiner and bring out each TX frequency separately and then use a proper isolated TX combiner such as the Rad TX-1 or Shure PA821.

See the paper on combining BTR on my website downloads page.  http://www.bestaudio.com/s/BTR_antenna_extend_coverage.pdf
Great paper Pete. Already referred to it when I had a similar setup to the one Keith is talking about.

I had a PA821 combiner and UA845 active splitter, and some passive ones also just in case.

Ended up bypassing the combiner because the production only needed one listening channel for all 8 belt packs.

Sent from my Xylophone using Tapatalk...

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Diogo Nunes Pereira

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Re: BTR 800 antenna combining
« Reply #4 on: September 16, 2016, 04:47:17 pm »



Thinking of the Shure UA221 and 6 db omni antennas of the appropriate frequency range.

In a similar setup I ended up using passive Shure paddles (LPDA) with good results. Too wideband but worked fine. I could get some more range with them than with the standard dipole.

Are these 6dB omnis custom build colineals for both frequency ranges? If so, who makes them?

I know of an antenna manufacturer here  in Spain but not much else.

Sent from my Xylophone using Tapatalk...

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Keith Broughton

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Re: BTR 800 antenna combining
« Reply #5 on: September 16, 2016, 06:40:01 pm »

Rx is not a problem.  You might experience excessive intermod combining the "already combined internally" TX frequencies with another Base.  Won't hurt but you might need to fiddle with freqs and might affect other wireless.

Correct way is to bypass the internal combiner and bring out each TX frequency separately and then use a proper isolated TX combiner such as the Rad TX-1 or Shure PA821.

See the paper on combining BTR on my website downloads page.  http://www.bestaudio.com/s/BTR_antenna_extend_coverage.pdf
So, by extension, combining 2 Sennhesiser IEM TX combiners into 1 antenna with a passive combiner should be avoided.
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Keith Broughton

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Re: BTR 800 antenna combining
« Reply #6 on: September 17, 2016, 08:39:08 am »

Rx is not a problem.  You might experience excessive intermod combining the "already combined internally" TX frequencies with another Base.  Won't hurt but you might need to fiddle with freqs and might affect other wireless.

Correct way is to bypass the internal combiner and bring out each TX frequency separately and then use a proper isolated TX combiner such as the Rad TX-1 or Shure PA821.

See the paper on combining BTR on my website downloads page.  http://www.bestaudio.com/s/BTR_antenna_extend_coverage.pdf
Interesting read.
I understand that splitting antennas is not an issue but could to go into a bit more detail on why combining already combined TX signals is problematic?
Just trying to get a clearer picture of what is going on.
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Jason Glass

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Re: BTR 800 antenna combining
« Reply #7 on: September 17, 2016, 10:45:31 am »

So, by extension, combining 2 Sennhesiser IEM TX combiners into 1 antenna with a passive combiner should be avoided.
Not necessarily. A passive combiner with decent isolation specs (around 30dB) can work very well in this application, if your system can afford the loss of 3dB per two-way coupling.

It helps to think of TX combining in terms of proper gain staging and component isolation. Most high quality active IEM/RFPL combiners have a signal path that looks roughly like this:
Input> isolator> amplifier> isolator> passive combiner> isolator> output. Each design may have fewer isolators than shown here, and may include other components such as filters or AGC circuits, and the designs vary due to cost, size, and weight considerations.

An overlying design consideration for off the shelf wideband active combining systems is the concept that each carrier is individually amplified to compensate for all losses incurred by subsequent passive stages. This is partly because amplifiers with high enough linearity to handle multiple carriers are prohibitively expensive.

The best active combiners have high isolation between all of their internal signal paths and all of their external ports. When you add a passive combiner after a typical IEM active combiner, isolation between the active components is maintained.

The amps in our active combiners can't handle an input with multiple carriers, such as BTR-800's combined 2ch output, without generating excessive IMD products.  Additional noise may also be generated by the transmitters when they are poorly isolated, and this noise is subsequently amplified by the active combiner.

One more note on combining BTR-800; turning one base station transmitter off via the front panel controls doesn't work when you intend to combine the output. All this does is unlock the PLL tuning and you end up with RF noise problems. To do this properly, you must open the chassis and disable the transmitter via the slide switches on the PCB.



Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Pete Erskine

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Re: BTR 800 antenna combining
« Reply #8 on: September 17, 2016, 03:27:25 pm »

So, by extension, combining 2 Sennhesiser IEM TX combiners into 1 antenna with a passive combiner should be avoided.

I have done it both ways but separate antennas are best.  The real problem is active combining of an active combiner output which is the BTR.  The BTR combiners have little if any filtering and therefore are particularly bad at rejecting other freqs coming in the out.
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Keith Broughton

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Re: BTR 800 antenna combining
« Reply #9 on: September 19, 2016, 03:56:18 pm »

As further info and practical gig requirements come to light, I have a good solution. The 2 BTRs only need to service 2 separate channels of com.
There is a way to connect the 2 BTR base stations to allow integration of audio.
Turning off the TXs on one station then allows the other station to TX the 2 channels with the use of only 1 TX antenna. No combiner required.
Each station must still get an RX signal and that could be done with 1 antenna and a splitter.
There is a bi-directional log periodic available that might proove useful in this particular application. Could also use the Shure UA860SWB omni antenna.

On a further note relating to passive combiner isolation numbers, the Shure UA221 device has 20 db, the Telex APS1 has 26 db and I can't find data on the Sennheiser ASP 212.
The Telex unit gets closest to the 30 db mark the passive combining of the 2 Sennheiser IEM 4 ch combiners.
For most applications, I can use 2 separate log periodics but sometimes bands just have to have the helical and there is only 1 available.
Maybe I'm wrong but I just don't see the point of using the helical 25' away from the band on a small stage. ::)

Thanks for the input  :)

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Re: BTR 800 antenna combining
« Reply #9 on: September 19, 2016, 03:56:18 pm »


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