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Live sound, AV and production techniques for House of Worship applications. Weigh in with your opinions on any SR gear you use, and find out what others have to say.
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Home » Church Sound » Church Sound » antenna management question
| antenna management question [message #125930] |
Wed, 14 May 2008 23:29  |
 Brian Murphy
Messages: 44
Registered: February 2008
Location: Colorado |
Member |
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We are in the process of upgrading our Church's sound system. We are a mobile church and setup / tear down each week. Prior to the new system, we use to set the 2 Sennheiser EM100 receivers on top of the board (it had room at the top). We can't do that with the new board. In addition, we are looking at adding up to 4 Sennheiser wireless IEM transmitters. That would put us up to having 6 boxes with 12 antennas.
We have room in the equipment rack for rack mounting the transmitters / receivers (using combinations of the GA2 rack mount), but I'm struggling with what to do with the antennas. One of our current receivers is in the 700MHz range and the other is in the 529MHz range. We'll pick the new wireless IEM transmitters in one of the frequency bands not in the 700MHz area.
How would you manage the antennas? Would you just get some BNC cables and mount the antennas on the back of the mobile rack? Do you like the antenna distribution system available?
Thanks
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| Re: antenna management question [message #125935 is a reply to message #125930 ] |
Thu, 15 May 2008 08:00  |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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First off, the best scenario is to get the antennas, receivers and IEM transmitters as close to the performance area as possible: RF free air path loss and coax attenuation is far greater than audio level attenuation down a snake.
That said, with only two wireless mic receivers, buy two passive two-way splitters (one for each diversity side, two passive LPDA (directional paddle) antennas and two appropriate lengths of high quality low loss coax. Mount the antennas atop mic stands so that they will always be high enough to have clear line of sight to the stage. Connect the antennas to the splitters via the high quality coax. Use coax jumpers from the splitter to the receivers. Keep the two antennas separated by at least six feet.
With reqards to the IEMs, buy a high quality active TX combiner such as the PWS GX-4, Shure PA821 or Sennheiser AC3000, a circular polarized antenna (either the PWS Helical or Sennheiser A5000-CP) and high quality low loss coax of the appropriate length. Again, use a mic stand for the antenna to get it up high enough to achieve an unobstructed line of sight to the performers. Or maybe C-clamp it to a structural member of your mobile stage. Try to keep this antenna at least 6-8 feet away from either receive antenna.
Try to establish two frequency groups; one being the wireless mic frequencies with about 400kHz per channel minimum, and the second being the IEM frequencies with about 800kHz per channel minimum. Try to keep a minimum of 2MHz between the two groups, and of course run complete intermod calculations creating a couple of coordinated groups, with spare frequencies in each, based upon where you typically operate.
Henry Cohen
Production Radio Rentals
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| Re: antenna management question [message #125943 is a reply to message #125941 ] |
Thu, 15 May 2008 18:46 |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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| Brian Murphy wrote on Thu, 15 May 2008 18:40 |
Do you have a specific brand of high quality low loss coax that you prefer?
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Any braid over foil double shielded construction. Manufacturers include Belden, Times Microwave, Canare and Gepco. For short runs (under 50'), a .250"(ish) diameter coax will be fine; RG-8X type or RG-6. Just make sure the coax impedance matches the impedance of any passive transmission path components used, such as the two way splitters.
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As far as the antennas for the receivers, we've been getting good reception so far with the built in antennas on the receivers. If we mount the receivers in the rack and then mount the antennas on the top of the rack somehow, connected with the high quality low loss coax, would that suffice or do you think a pair of Sennheiser A2003-UHF directional antennas would be needed?
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You can't simply take the 1/4 wave whips from the back of the receiver and remote them: They need the ground plane of the receiver chassis for proper matching. You'll need to move to a dipole design, be it omnidirectional or directional. So yes; the Sennheiser A2003-UHF is appropriate and preferred.
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The transmitter combiners seem very expensive. They appear to be perfect for what we want to do, but the cost will prohibit their use. I suppose this is another case for the remote mount original antennas and high quality low loss coax.
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Again, you can't simply remote mount a 1/4 wave antenna without making an appropriate ground plane. For the 600MHz range, a 12" metal speaker grill works well. However, given the propagation path you need, the Sennheiser directional paddles again would be the preferred option. But the other problem is having four transmit antennas: The signals from any three transmitters will go down the antenna of the fourth and cause intermodulation problems in the final RF stage if too close together. You'll need to spread the TX antennas out, probably around 5 - 6 feet from one another.
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I think I follow the discussion on keeping the frequencies apart, but I'm not following the "intermod calculations" part. Is there some easy-to-follow documentation on that or a quick explanation of what to do here? We already have our wireless microphones and will be adding in 2 to 4 IEM transmitters.
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Very simple - When multiple carriers enter a non-linear transmission path (like an antenna distribution multicoupler or the front end of a receiver) they will mix producing additional unwanted and potentially destructive frequencies (intermodulation products) if too close to one of your chosen frequencies. This mixing occurs according to very simple math:
f1+f2-f3
f1-f2+f3
f2-f1+f3
2f1-f2
2f1-f3
2f2-f1
2f2-f3
2f3-f1
2f3-f2
Repeat for every combination of three frequencies. These 3rd order IM products are the most destructive, but in reality *all* frequencies will mix. Obviously this is a lot of math, which is why there are IM computer programs to do the calculations. Sennheiser SIFM is the best of the free offerings. Talk to your dealer or an RF consultant.
Henry Cohen
Production Radio Rentals
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| Re: antenna management question [message #125946 is a reply to message #125930 ] |
Fri, 16 May 2008 11:17 |
Karl P(eterson)
Messages: 316
Registered: April 2004
Location: Atlanta, GA |
Has No Life |
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I guess I don't understand what is going on in your guys heads.
Most of us in HOW environments that are using wireless are doing it for our "money channels". Knowing this you are then trying to devise ways to stray from industry standard and accepted practice?
I understand that you may not have realized how much wireless costs beyond just buying a TX/RX pair, but that doesn't excuse you from doing the right thing now.
If you can't afford the correct infrastructure, maybe you should scale your system size down, get your infrastructure set now, then add as you need them in the future.
It would be one thing if we were using wireless on a bunch of stuff that doesn't matter and we could stand to loose, but that is normally not the case with RF in HOW, so I would _strongly_ recommend you do the right thing and get proper antenna, cable, and distribution in your systems, even if you have to make your systems smaller in the process to afford it.
Karl P
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| Re: antenna management question [message #125947 is a reply to message #125930 ] |
Fri, 16 May 2008 11:30 |
Jeff Ekstrand
Messages: 262
Registered: January 2008
Location: Chicago, IL |
Has No Life |
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I agree with Karl.
There is no reason to give up future functionality, and/or neuter the quality of your system by straying from the proper infrastructure at this juncture.
Another thought, given the white spaces, is to hold-off on buying any additional wireless until we see what happens with he DTV revolution in February '09. Personally, I've got the budget to add a couple channels of wireless, but I've told our staff (I'm just a volunteer at this church who has the privilege of spending money) that we're not going to buy additional wireless until we see what works in 9 months, one year, etc.
Can you survive with your current two wireless systems, set-up on a side-table or a flight case stack for the time being?
Those are my two strong suggestions.
1. Don't give-up on infrastructure now and suffer later
2. Hold-off on purchasing wireless until each of us learns what effect the White Spaces issue will have on us individually. If you must purchase wireless, do some research first and get the right product, even if it means it doesn't match what you have now.
As for the original question of antenna maintenance, I think the antenna distribution systems are definitely the way to go. They clean-up the rack, and your rig looks a lot more professional and presentable with only two antennas (maybe four if you have enough receivers).
Jeff Ekstrand
Event Production Manager
Christian Heritage Academy, Northfield, IL
FOH Coach/Engineer, Special Projects Manager
Willow Creek Community Church, North Shore Campus, Northfield, IL
"Why should God settle for less than the best?"
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| Re: antenna management question [message #125949 is a reply to message #125930 ] |
Fri, 16 May 2008 12:26 |
Brian Murphy
Messages: 44
Registered: February 2008
Location: Colorado |
Member |
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<edited post - I removed much of what I've said in this reply - there were two other replies posted before I typed this - I need to read and digest them. Sorry>
[Updated on: Fri, 16 May 2008 12:45]
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| Re: antenna management question [message #125952 is a reply to message #125947 ] |
Fri, 16 May 2008 13:13 |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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| Jeff Ekstrand wrote on Fri, 16 May 2008 12:30 |
Another thought, given the white spaces, is to hold-off on buying any additional wireless until we see what happens with he DTV revolution in February '09. Personally, I've got the budget to add a couple channels of wireless, but I've told our staff (I'm just a volunteer at this church who has the privilege of spending money) that we're not going to buy additional wireless until we see what works in 9 months, one year, etc. . . .
. . . Hold-off on purchasing wireless until each of us learns what effect the White Spaces issue will have on us individually. If you must purchase wireless, do some research first and get the right product, even if it means it doesn't match what you have now.
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If one needs additional channels of wireless now, I wouldn't be that concerned with the spectrum issues. Stay within 470-698MHz (512-698MHz if in one of the 13 major economic markets and the gulf states using T-band two way radios) and you'll avoid most of the future problems. If whitespace devices are eventually approved, there's nothing you can do about it anyway. If budget permits, you could also look at the Lectrosonic and Sennheiser 944-952MHz STL band offerings.
| Brian Murphy wrote on Fri, 16 May 2008 13:26 |
The Sennheiser A2003-UHF antenna is about $250-$280. I'd really like to not have to spend an extra $500 if we don't need to. I've already had to cut way back on the equipment I want because of our Church's budget. The Sennheiser A1031-U is a little more reasonable ($150 or so each)
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Unfortunately, physics doesn't concern itself with budgets. Why would you want to use an omnidirectional antenna when all the RF energy of interest is 50' in front of you in a relatively confined area (the stage)?
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Our mobile rack has the rack mount rails in the front and back, if I get a 3 or 4 space tall piece of metal and mount that to the back of the rack, drill a few holes and remote mount the 1/4 wave antennas there, would that work as a ground plane?
As far as the transmitters go, if we only have 2 IEM transmitters, would remote mounting the 1/4 wave antennas similar to what I have listed above work?
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The ground planes have to be horizontal, bonded to the coax shield very well and the diameter of the ground plane needs to be at least 1/2 wave length of the lowest frequency the system can tune to. Keep all antennas at least 5-6 feet apart unless you have very high Q external filters.
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Is the problem only when you get above 3 transmitters?
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No. All you need is two frequencies to start mixing and create intermodulation products.
Henry Cohen
Production Radio Rentals
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| Re: antenna management question [message #125954 is a reply to message #125930 ] |
Fri, 16 May 2008 13:31 |
Brian Murphy
Messages: 44
Registered: February 2008
Location: Colorado |
Member |
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Henry, Karl, Jeff,
Thanks for the help. I'm really trying to make sure I do the right thing with setting up our wireless and buying the right equipment. I've definitely learned from this board that some things are worth spending the money on to do right the first time. I've also learned that there are some things where you can spend less and have completely acceptable results, but spending more buys convience or professional and more presentable results. I'm trying to make sure I have the right balance with my small budget.
Right now, our current wireless microphones and receivers work fine. We put them either on top of the old mixer rack or on a table next to the rack. One was a C-Range and the other an A-range. With these two items, buying a Sennheiser G2 Antenna splitter kit (for around $1000) didn't seem right because they appear to be tuned to a particular range.
We could look at getting a pair of the directional Sennheiser A2003-UHF or the omni-directional A1031-U antennas and a splitter to go to the two receivers - would that be an acceptable solution? How wide is the pattern on the directional antennas? Our pastor likes to move around a lot and sometimes wanders out into the congregation with a wireless microphone (he has gone as far as having people who are to my far left or right talk).
The Sennheiser AC3000 is far to expensive for what we want to do. The Sennheiser AC2/NT3 at around $700 may be within reach. It is an active 4:1 antenna combiner. Right now, we only plan on buying two IEM transmitters, but we do eventually plan to go to 4. Would this also require one of the Sennheiser A1031-U antennas?
And just to make sure I understand, what would you consider the lowest price acceptable solution for the two existing wireless microphones and adding two IEM transmitters? Would it be acceptable to stack the two wireless mic receivers and sit them on a table on the left of the mixer rack and stack the two IEM transmitters and stick them on a table on the right of the mixer rack? I'm not just trying to be cheap here. I really am trying to understand what the minimums are. If doing this is bad for a reason other than convenience or looks, then I'd want to know. If it is Ok to do, I'd also want to know. I'm making an assumption here that moving up to more than the 2 wireless mic receivers and 2 IEM transmitters would definitely require antenna splitters and combiners, etc.
Right now, I'm leaning towards 2 Sennheiser A1031-U antennas split for the two wireless mic receivers, a Sennheiser AC2 antenna combiner for the 2 IEM transmitters. I don't know what to do for an antenna for the AC2.
Thanks
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| Re: antenna management question [message #125955 is a reply to message #125954 ] |
Fri, 16 May 2008 14:36 |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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| Brian Murphy wrote on Fri, 16 May 2008 14:31 |
Right now, our current wireless microphones and receivers work fine. We put them either on top of the old mixer rack or on a table next to the rack. One was a C-Range and the other an A-range. With these two items, buying a Sennheiser G2 Antenna splitter kit (for around $1000) didn't seem right because they appear to be tuned to a particular range.
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For only two receivers, use a passive two way splitter such as the Mini-Circuits ZSC-2-4 (50 ohm) (http://www.minicircuits.com/pdfs/ZSC-2-4.pdf); $53.00 each. This is a better method than a powered splitter and you can use the savings to put towards a proper transmitter combiner.
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We could look at getting a pair of the directional Sennheiser A2003-UHF or the omni-directional A1031-U antennas and a splitter to go to the two receivers - would that be an acceptable solution? How wide is the pattern on the directional antennas? Our pastor likes to move around a lot and sometimes wanders out into the congregation with a wireless microphone (he has gone as far as having people who are to my far left or right talk).
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From the sounds of it, you probably are better off with the omni. The directional antenna has a usable horizontal beamwidth of about 100 degrees.
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The Sennheiser AC3000 is far to expensive for what we want to do. The Sennheiser AC2/NT3 at around $700 may be within reach. It is an active 4:1 antenna combiner. Right now, we only plan on buying two IEM transmitters, but we do eventually plan to go to 4.
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There's a reason the AC3000 costs a couple of thousand more than the AC2. Better IM suppression and higher saturation point. | Quote: |
Would this also require one of the Sennheiser A1031-U antennas?
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Depends: Do you need omnidirectional or directional coverage?
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Would it be acceptable to stack the two wireless mic receivers and sit them on a table on the left of the mixer rack and stack the two IEM transmitters and stick them on a table on the right of the mixer rack?
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If you're remoting the antennas, then you can stack the receivers together. Same with the IEM transmitters, except that I would keep some space between them and the receivers in case there's a bit of RF leakage from the transmitters.
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I don't know what to do for an antenna for the AC2.
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Your antenna selection is based on the coverage pattern required.
Henry Cohen
Production Radio Rentals
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| Re: antenna management question [message #125969 is a reply to message #125964 ] |
Sun, 18 May 2008 08:48 |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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This arrangement should work for you; good plan on the IEMs being on stage, on opposite sides. Just spread the receivers out as much as you can to keep the antennas clear of each other (nearfield interactions can occur within a couple of wavelengths - about 48" at 650MHz). Still perform intermod calculations to mitigate any self-induced interference issues.
Henry Cohen
Production Radio Rentals
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| Re: antenna management question [message #125997 is a reply to message #125991 ] |
Wed, 21 May 2008 09:57 |
Henry Cohen
Messages: 90
Registered: January 2006
Location: Westchester Co. |
Nothing Better To Do |
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| Brian Murphy wrote on Tue, 20 May 2008 17:13 |
I have a few more questions:
- Is the ASP2/NT1 antenna splitter something that covers the whole 400MHz-900Mhz spectrum or would I need a separate one for each of my wireless microphones?
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According to the data sheet, 500-870MHz. But more importantly this unit has far more loss than a simple 4 way passive splitter; 14dB for the Sennheiser versus 7ish dB for a typical Mini-Circuits splitter at one tenth the price.
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- I understand that the AC3000 is several thousand more than the AC2, however, I don't think I understand the base AC2 quality level. Is using an AC2 going to provide as good or better quality than the EW300 IEM transmitters individually or would using the AC2 actually degrade the performance compared to not using a transmitter combiner?
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Tough to tell; if the AC2 is built cheaply enough where the front end saturates (overloads) and starts to produce harmonics, or the amplifier stage produces strong enough IM products, the result will be worse than not using it. The only way to know for sure is to build up a system and look at it on a spectrum analyzer.
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I'm trying to decide now if we can put the receivers in the mixer rack with an ASP2/NT1 and a pair of A1031-U antennas and put the IEM transmitters in the amp rack on stage with the AC2/NT3 and a single A1031-U antenna.
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As long as you get the antennas up high above the rack and all other equipment, sounds good.
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Also, in the amp rack for the IEM transmitters, if we mounted the AC2 on the back of the rack, could I use the normal antenna that comes with the EW300 and connect it to the AC2?
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I wouldn't recommend it. My guess is the AC2 is not very well shielded and the RF energy coming off the antenna could interact with the internal transmission path traces. Better to use a remote dipole antenna or create a ground plane for the OEM antenna.
Henry Cohen
Production Radio Rentals
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