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Author Topic: Large RF coverage area, multiple antenna's  (Read 3868 times)

Pete Erskine

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Re: Large RF coverage area, multiple antenna's
« Reply #10 on: December 22, 2013, 04:45:01 pm »

What would the best way to combine 4 antennas into one distro, in order to provide coverage for an extremely wide area.

I have been quite successful in using multiple RX and TX antennas in one venue.  To keep the Diversity you need to cover each area with the 2 channels of antennas and the antennas need to be at lease 6-30' apart - say on each side of the stage.

Multiple RX antennas in one zone do not cause dropouts, it only increases the signal so there is no need to be particularly careful in overlapping the coverage.  For transmit systems minimum overlap is desirable but also has little bad effect.

The entire trick is managing the levels from your antennas.  Long Coax introduces loss and in many locations you can use an amplified +10dB antenna to make up.  In Hi RF level areas, though, amplified antennas cannot be used at all because they overload.  Areas such as 34th street near Macy's In NYC which is less than a mile from the Empire State Building TV antennas.

Splitters and combiners need to be best quality with minimum loss.  My favorites come from Mini circuits.  A 1X 2 splitter at 600 mHz has about 3.5 dB loss.

Another terrific new tool is RF over fiber.  It is not for the novice to use and requires a lot of careful RF level wide band measurements covering all the concurrent carriers which will be carried on the fiber.  The advantage is no loss!

Here are a layout for multiple antenna system transmit and RX system which was not for Mics nor was diversity.  Same could be applied to a diversity system but double.

« Last Edit: December 22, 2013, 04:49:41 pm by Pete Erskine »
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Jason Glass

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Re: Large RF coverage area, multiple antenna's
« Reply #11 on: December 23, 2013, 12:26:07 pm »

Pete, thanks for posting that.  Fantastic info!

I have been quite successful in using multiple RX and TX antennas in one venue.  To keep the Diversity you need to cover each area with the 2 channels of antennas and the antennas need to be at lease 6-30' apart - say on each side of the stage.

Multiple RX antennas in one zone do not cause dropouts, it only increases the signal so there is no need to be particularly careful in overlapping the coverage.  For transmit systems minimum overlap is desirable but also has little bad effect.

The entire trick is managing the levels from your antennas.  Long Coax introduces loss and in many locations you can use an amplified +10dB antenna to make up.  In Hi RF level areas, though, amplified antennas cannot be used at all because they overload.  Areas such as 34th street near Macy's In NYC which is less than a mile from the Empire State Building TV antennas.

Splitters and combiners need to be best quality with minimum loss.  My favorites come from Mini circuits.  A 1X 2 splitter at 600 mHz has about 3.5 dB loss.

Another terrific new tool is RF over fiber.  It is not for the novice to use and requires a lot of careful RF level wide band measurements covering all the concurrent carriers which will be carried on the fiber.  The advantage is no loss!

Here are a layout for multiple antenna system transmit and RX system which was not for Mics nor was diversity.  Same could be applied to a diversity system but double.

peter dakin

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Re: Large RF coverage area, multiple antenna's
« Reply #12 on: January 28, 2014, 06:49:21 am »

How big of an area are you actually trying to cover?

Adding more antennas will likely create more trouble than good for you, as the signal coming to each antenna will interfere with the other by just raw combining them. 

An alternative would be placing additional receivers tuned to the same frequency to cover each specific area, and then activating the receiver on the mixer closest to the mic user.
Area was 90-140m wide and 10m-15m deep. However the stage area was in the centre and only real logical position for antenna's.
This was a quick fire Q&A event, with 32 romaing mics, for about 3000 people on tiered seating. There would be no time to decided which receiver to go wth, sadly.

Giving Shure a call isn't a bad idea.

Pete Erskine, sounds interesting, will investigate into your suggestions.
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Chris Johnson [UK]

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Re: Large RF coverage area, multiple antenna's
« Reply #13 on: January 28, 2014, 08:01:46 am »

90-140m x 10-15m doesn't seem to big to me.
If you can put your antennae somewhere with line of sight to all (at least most) of the room, then I'd be tempted to up your HH Tx to 50mW/100mW and go from there.

Alternatively, 2 pairs of Rx antennae (LPDA-type) at each end of the long space, over fibre (to minimise RF loss on cabling), combined back at the receivers to feed your distributors A and B antenna inputs.
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Keith Broughton

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Re: Large RF coverage area, multiple antenna's
« Reply #14 on: January 28, 2014, 09:01:55 am »

Pete, could you clarify the use of more than 1 RX antenna in the same coverage area?
I was under the (mistaken?)impression that if 2 antennas (that combine at the same receiver) were used over the same area, there might be phase cancellations possible.
However, in a diversity system , this might not be a problem.
The reason I ask is that I have a job that requires coverage of a hockey rink but I have to have the antennas down below the edge of the boards. (no other option) in a fairly congested RF environment.
A diversity pair at each end might give me the results I need but I have been reluctant to try.
Any insights would be appreciated.
Also, could you give the model of equipment to do Rf over Fibre?
« Last Edit: January 28, 2014, 09:09:39 am by Keith Broughton »
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Pete Erskine

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Re: Large RF coverage area, multiple antenna's
« Reply #15 on: January 28, 2014, 01:53:27 pm »

Pete, could you clarify the use of more than 1 RX antenna in the same coverage area?
I was under the (mistaken?)impression that if 2 antennas (that combine at the same receiver) were used over the same area, there might be phase cancellations possible.
However, in a diversity system , this might not be a problem.
The reason I ask is that I have a job that requires coverage of a hockey rink but I have to have the antennas down below the edge of the boards. (no other option) in a fairly congested RF environment.
A diversity pair at each end might give me the results I need but I have been reluctant to try.
Any insights would be appreciated.
Also, could you give the model of equipment to do Rf over Fibre?

There is no issue with using multiple RX antennas in same area.  Get you antennas high enough for good line of sight.  Covering a football field size area from one side is no problem if your frequencies are clean.  If you want put the 2 diversity antennas on each end of the fiels (2 on each channel)  Use +10 dB antennas on the cables which are over 200' long.
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Keith Broughton

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Re: Large RF coverage area, multiple antenna's
« Reply #16 on: January 28, 2014, 05:35:40 pm »

There is no issue with using multiple RX antennas in same area.  Get you antennas high enough for good line of sight.  Covering a football field size area from one side is no problem if your frequencies are clean.  If you want put the 2 diversity antennas on each end of the fiels (2 on each channel)  Use +10 dB antennas on the cables which are over 200' long.
Thanks for the info.
The particular hockey rink application doesn't allow for any antennas in any kind of line of sight do I had to work out something.
I got pretty good results with log periodics against the boards at one end but I think antennas at the other end as well would be helpful.
Dodgers stadium was absolutely jammed with DTV signals so it was a real trick to find some clean spaces!
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Pete Erskine

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Re: Large RF coverage area, multiple antenna's
« Reply #17 on: January 28, 2014, 09:32:23 pm »

The particular hockey rink application doesn't allow for any antennas in any kind of line of sight d

Tell them that that is unacceptable.  No line of sight - NO RF.  They wouldn't put that restriction on the lighting equipment - same is true for Antennas.  Stand your ground.
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Tom Bourke

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Re: Large RF coverage area, multiple antenna's
« Reply #18 on: January 28, 2014, 10:40:51 pm »

On the other option of two receivers would using something like the shure scm810 smart mixer be able to detect the level of the receivers and activate the best signal.  Also providing the fail over with automatic switching.
I have seen this work very well.  It was used for a casino where they wanted 1 mic to work everywhere.  Not sure how well it would work for multiple mics in different coverage areas.
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Pete Erskine

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RF over fiber
« Reply #19 on: January 28, 2014, 11:52:35 pm »

Also, could you give the model of equipment to do Rf over Fibre?

RF over fiber is terrific but needs a lot more engineering to make it work well.  First is determining the transmit RF level to put into the hardware.  If you are only sending 1 carrier it's easy - measure the RF power and pad it down to 0dBm.  If you are using multiple carriers you need to set your RF Power meter to include the entire bandwidth and measure with all carriers on at the same time and pad it down to 0 dBm.

Simple Spectrum analyzers will not work.  A R&S FSH3 will measure power levels.

The automatic level control compensates for some level differences in the RF levels.

RX Fiber is easier since unless your Walkie talkie or your wireless mic is really close next to the RX antenna you wont be getting over 0dBm.

Here is a nice but expensive package from Riedel Communications.  The fiber cable between the fiber TX and fiber RX needs to be single mode Angle Polished Connector or APC.  Normal Single mode will not work very well if it has flat polished connectors.

RF over fiber usage PDF
« Last Edit: January 28, 2014, 11:56:31 pm by Pete Erskine »
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