Wireless How to set up directional antennas

[zuixro]

I know there have been a lot of wireless mic threads lately, and everyone's probably tired of them, but I have a question about directional antennas.

(Yes, it's antennas when it's radio, antennae is biology, Antenna - Wikipedia, the free encyclopedia , I just learned that)

We are getting a new wireless mic system soon (Hopefully Shure UHF-R, but probably ULXP). I was looking at permanently (or semi-permanently) mounting directional antennas in our space.

I've seen at least three different configurations for directional antennas:

1. Several feet apart, one a few feet higher than the other. This one was used parallel to the stage.

2. Right next to each other, one turned at a right angle to the other.

3. Spaced 20+ feet apart and pointed at the stage.

Which is the best way to set up the antennas? (or does it depend on the circumstances) Is there anything wrong with any of these? Number 2 seemed a little weird to me, but I can see how it would work. I don't know what the vertical spread is on these antennas are, but if it's small, that could help.

By the way the antennas I am talking about are like this:
Shure UA870USTV UHF Antenna,Wide Band 470-698 | Full Compass

I was thinking about setting up the antennas like this:

Blue dots are antennas, blue lines are where they are pointed.

They would be about 60 feet apart, 25 feet above the deck, and 60-100 feet from the transmitters (these measurements are rough, I'm going by the drawing on our website, and having to figure out some unwritten dimensions)

If that doesn't look good, what is the ideal spacing between the antennas? (I suspect it has more to do with the angle and where they "converge" than the actual spacing) We have a long, narrow wooden wall along the back so we can mount them any distance apart. (actually we will probably end up putting them on mic stands on the balcony, but the question is the same)

I want to go with directional antennas because we had some RF problems with our last musical (probably from the TV station on campus, but I'm not sure).

 

[MisterTim]

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1. Several feet apart, one a few feet higher than the other. This one was used parallel to the stage.

2. Right next to each other, one turned at a right angle to the other.

3. Spaced 20+ feet apart and pointed at the stage.

If that doesn't look good, what is the ideal spacing between the antennas? (I suspect it has more to do with the angle and where they "converge" than the actual spacing) We have a long, narrow wooden wall along the back so we can mount them any distance apart. (actually we will probably end up putting them on mic stands on the balcony, but the question is the same)

I would say spatial diversity is the best option; I see it used the most indoors.

As far as spacing, the actual distance isn't important as long as it is a multiple of the wavelength range you are working in. For instance, if the median of the frequencies of your microphones is 500MHz, then your wavelength is 0.6m and you want the antennas to be 1.2m/1.8m/18m apart. Of course this becomes less important the further apart you get, because you have a greater margin of error due to the fact that your'e approximating the wavelength. But this is how I've always been told a spaced diversity system needs to be set up.

 

[FMEng]

We are getting a new wireless mic system soon (Hopefully Shure UHF-R, but probably ULXP). I was looking at permanently (or semi-permanently) mounting directional antennas in our space.

I've seen at least three different configurations for directional antennas:

1. Several feet apart, one a few feet higher than the other. This one was used parallel to the stage.

2. Right next to each other, one turned at a right angle to the other.

3. Spaced 20+ feet apart and pointed at the stage.

be about 60 feet apart, 25 feet above the deck, and 60-100 feet from the transmitters (these measurements are rough, I'm going by the drawing on our website, and having to figure out some unwritten dimensions)

If that doesn't look good, what is the ideal spacing between the antennas? (I suspect it has more to do with the angle and where they "converge" than the actual spacing) We have a long, narrow wooden wall along the back so we can mount them any distance apart. (actually we will probably end up putting them on mic stands on the balcony, but the question is the same)

I want to go with directional antennas because we had some RF problems with our last musical (probably from the TV station on campus, but I'm not sure).

Definitely option three. Vertical diversity won't do much unless the actor is in a helicopter, so that eliminates #1. Pointing the antenna sideways won't work because the antenna probably has a deep null in its pickup pattern at 90 degrees. That eliminates #2. What you want is horizontal space diversity.

Do keep in mind cable loss if the runs are long. The fatter the cable, the lower the loss. Match cable impedances to the antenna system. For a 50 ohm system, that means RG-8 size, with a foil and braid shield.

If you have a TV broadcast transmitter nearby, you probably need to filter it out to prevent receiver desense. Chances are the TV transmitter and the mics share the same band, and the poor little mic receiver can't handle a 100,000 Watts blasting it. It's like trying to hear a pin drop with a jack hammer by your ear. The antennas may not help (or make it worse) if this is the situation. In fact, if the TV transmitter is nearby, do NOT use an active or amplified antenna like the one you show. The internal amp can overload. Instead, use passive antennas and in-line filters.

The TV engineers can help you get the right filters to go between antenna and splitter. Even if the TV studios are on campus, ask where the transmitter is. It may not be nearby, and the tower on campus could be just for microwave link. The FCC database shows the WRET channel 43 tower at Croft State Park, near Pacolet, but I may have guessed the wrong station.

 

[zuixro]

Definitely option three. Vertical diversity won't do much unless the actor is in a helicopter, so that eliminates #1. Pointing the antenna sideways won't work because the antenna probably has a deep null in its pickup pattern at 90 degrees. That eliminates #2. What you want is horizontal space diversity.

Do keep in mind cable loss if the runs are long. The fatter the cable, the lower the loss. Match cable impedances to the antenna system. For a 50 ohm system, that means RG-8 size, with a foil and braid shield.

If you have a TV broadcast transmitter nearby, you probably need to filter it out to prevent receiver desense. Chances are the TV transmitter and the mics share the same band, and the poor little mic receiver can't handle a 100,000 Watts blasting it. It's like trying to hear a pin drop with a jack hammer by your ear. The antennas may not help (or make it worse) if this is the situation. In fact, if the TV transmitter is nearby, do NOT use an active or amplified antenna like the one you show. The internal amp can overload. Instead, use passive antennas and in-line filters.

The TV engineers can help you get the right filters to go between antenna and splitter. Even if the TV studios are on campus, ask where the transmitter is. It may not be nearby, and the tower on campus could be just for microwave link. The FCC database shows the WRET channel 43 tower at Croft State Park, near Pacolet.

I was going to go with Shure's 100ft BNC cable, I don't know what type of cable it is though. I'll look in to some RG-8. Shure's Wireless Accessory Wizard says to use the +10dB amplifier on the antenna for a 100ft run.

Looking at Google Earth, the transmitter is about 12 miles away, so I guess that's not the cause of the problems. It was probably just the old gear we had. (old fixed channel Shure wireless, they are in the legal band though, I want to retire them, but our TD is going to hang on to them until they fall apart)

If we do go with ULXP, we will get the J1 band ones, 556-589MHz (that has the most open frequencies). The WRET transmitter is 644-650MHz. Being 12 miles away, it doesn't seem like it would cause problems, but then again, I'm not the radio expert. Would it be safe to use an amplified antenna that close? We rented some mics (with amplified antennas) for our last musical. The guy that set them up did research to make sure that none of the frequencies collided with anything nearby.

I was just about to look up where the transmitter was, but you beat me to it. Thanks. There's an antenna tower on campus, I haven't looked closely at it, but I guess it's just a cell tower. There's also a big dish, but it looks disused.

 

[techfreek]

We have a very similar system, for our we have ours similar to #3, but due to a poorly designed theater, our booths are separate, and thus we put both in front of the sound booth, so they are only about 4-5 feet apart. We did not really research exactly where TV broadcast stations are, but a local sound company who helped us order it and assist with the install, told us the frequencies commonly used by radio and TV stations near by, and thus avoided those channels.

 

[museav]

It it at all viable to try to get the antennas closer to the stage? Assuming that is where the wireless transmitters are normally located it is almost always better to get the antennas closer to the transmitters, the losses from the transmitter to antenna are probably going to be greater for the same distance than the loss of a cable of the same length and the antennas further away from the transmitter increases the level of unwanted signals compared to the wanted signal.

 

[zuixro]

It it at all viable to try to get the antennas closer to the stage? Assuming that is where the wireless transmitters are normally located it is almost always better to get the antennas closer to the transmitters, the losses from the transmitter to antenna are probably going to be greater for the same distance than the loss of a cable of the same length and the antennas further away from the transmitter increases the level of unwanted signals compared to the wanted signal.

Good point. If we halve the distance from the transmitter to antenna, we gain 6dB right? The only problem is, we would have to add about 50ft of cable to it, and Shure's Wireless Accessory Wizard says we'd need amplifiers (Shure UA830USTV UHF Antenna Amplifier) for 150ft of cable. It's gonna depend on our budget in the end. I'm afraid I've already gone over budget with this system... (haven't bought anything yet, probably won't for a few months, but I can't get a hard budget number from the TD)

Those amplifiers would go immediately after the antennas right? Amplify the cleanest signal possible.

 

[Chris15]

I think we've established that spatial diversity is the prefered method.

Beyond I think about a wavelength, you don't get much more benefit from the diversity so you'd actually be better off moving the antennas closer together to reduce the cable lengths in my opinion. There are some exceptions, refer to Shure's antenna publication [pdf] for more details on placement.

I agree with Brad on wanting to get them closer to the stage. I don't know who I am quoting here but even the worst coax has less loss than free space. BUT, if moving the antennas results in substantially more electrical distance than the equivalent free space, you could end up with worse performance and what I mean there is if the coaxes are routed through conduits etc and end up going right round the edge of the space or something and you have 30m of cable vs say 15m Line of Sight distance.

mbenonis would suggest you steer away from active antennas and in schools and other places of similar long term skill level I do too. You are better off spending the money on a quality cable than on an amplifier. While you SHOULD use 50 ohm coax, the reality is that the antenna is not 50 ohms and the receiver front end is not 50 ohms and so a 75 ohm coax will normally work fine. You get a maximum of about 1dB of loss from the impedance mismatch. All that however is out the window when transmitting...

With respect to MisterTim being spaced at exact wavelength multiple is actually not preferred basically because any standing waves that are created will be present at every half wavelength... Oh and which half wavelength of the n systems in use should we go for?

 

[MisterTim]

With respect to MisterTim being spaced at exact wavelength multiple is actually not preferred basically because any standing waves that are created will be present at every half wavelength... Oh and which half wavelength of the n systems in use should we go for?

Meh well then disregard what I was saying in a year or two I'll have the college classes under my belt to understand this stuff on my own instead of relying on 'trusted' sources...

 

[mbenonis]

Looks like I'm late to the party here! Cut me a bit of slack; I spent the night on a mountaintop for ARRL Field Day trying (and failing) to work amateur satellites... Not sure what that says about me, but oh well.

Here's my two cents:

Definitely option three. Vertical diversity won't do much unless the actor is in a helicopter, so that eliminates #1. Pointing the antenna sideways won't work because the antenna probably has a deep null in its pickup pattern at 90 degrees. That eliminates #2. What you want is horizontal space diversity.

Agreed on spatial diversity. Re #2, in principle it's hard to say the exact polarization of the received signal. Sure, we try to orient the whips vertically, but who knows what happens when the actor gets on stage (never mind the reflections in the the space). Practically it probably won't make a heck of a lot of difference.

I guess this is a long way of saying it doesn't matter but you should think it through as a thought exercise.

Do keep in mind cable loss if the runs are long. The fatter the cable, the lower the loss. Match cable impedances to the antenna system. For a 50 ohm system, that means RG-8 size, with a foil and braid shield.

Definitely get the lowest loss cable you can afford. That would probably be RG-8/U (not RG-8X, which is thinner). That said, for 100' I would highly recommend stepping up to LMR-400 or similar (RG-213, etc). As a fallback, RG-6 isn't bad. It's 75 Ohm line, but then again your antenna won't be 50 Ohms, and your receiver front end probably won't be all that close either (though if you use an antenna distro, 50 Ohms probably isn't a bad approximation on that end). Make sure you use good quality connectors (BNC on both ends)--resist the urge to terminate in F connectors and use an adaptor.

If you have a TV broadcast transmitter nearby, you probably need to filter it out to prevent receiver desense. Chances are the TV transmitter and the mics share the same band, and the poor little mic receiver can't handle a 100,000 Watts blasting it. It's like trying to hear a pin drop with a jack hammer by your ear. The antennas may not help (or make it worse) if this is the situation. In fact, if the TV transmitter is nearby, do NOT use an active or amplified antenna like the one you show. The internal amp can overload. Instead, use passive antennas and in-line filters.

Going off the information posted after this, I agree on avoiding amplified antennas and/or preamps. I know Shure's site suggests it, but they aren't taking into account the possibility of the amplifier getting distorted. I would opt instead for really good coax and directional passive antennas (might look at the Lectrosonics ALP500, I think it is). You'll probably end up with a wash in terms of cost.

The TV engineers can help you get the right filters to go between antenna and splitter. Even if the TV studios are on campus, ask where the transmitter is. It may not be nearby, and the tower on campus could be just for microwave link. The FCC database shows the WRET channel 43 tower at Croft State Park, near Pacolet, but I may have guessed the wrong station.

If you go with J1 band, you probably won't have too much in the way of issues if you avoid wideband amplifier (see above). Though if it gets really rough you may need to do some filtering right at the antennas.

I was going to go with Shure's 100ft BNC cable, I don't know what type of cable it is though. I'll look in to some RG-8. Shure's Wireless Accessory Wizard says to use the +10dB amplifier on the antenna for a 100ft run.

Definitely avoid this. Shure's cable won't be nearly beefy enough, and like I said above the preamp is also no good with a local TV'er.

You know, I played with Shure's "Wireless Accessory Wizard." All it recommends are Shure parts. May as well call it the "Wireless Accessory Sales Wizard." Remember, folks, in general RF is RF is RF, and you can use whatever antenna, coax, amplifier, and splitter you want to regardless of manufacturer. (There are sometimes DC power issues for active devices like amplifiers, but if you follow the directions and know what you're doing it's never a big issue).

There's also a big dish, but it looks disused.

Could be the studio-transmitter link, either for the TV'er or perhaps the radio station. Hard to say without a picture though.

I agree with Brad on wanting to get them closer to the stage. I don't know who I am quoting here but even the worst coax has less loss than free space. BUT, if moving the antennas results in substantially more electrical distance than the equivalent free space, you could end up with worse performance and what I mean there is if the coaxes are routed through conduits etc and end up going right round the edge of the space or something and you have 30m of cable vs say 15m Line of Sight distance.

Agreed all around here. Sounds like something Henry Cohen, or maybe Jim Brown, might have said and/or written.

mbenonis would suggest you steer away from active antennas and in schools and other places of similar long term skill level I do too. You are better off spending the money on a quality cable than on an amplifier. While you SHOULD use 50 ohm coax, the reality is that the antenna is not 50 ohms and the receiver front end is not 50 ohms and so a 75 ohm coax will normally work fine. You get a maximum of about 1dB of loss from the impedance mismatch. All that however is out the window when transmitting...

Beat me to it.

You know, I really should get all of this into the FAQ at some point...maybe if people bugged me about it more it might get done sooner than later.

 

[WooferHound]

I have never seen the antennas placed in the audience area. I have always seen the antennas onstage usually at the monitor mix position. The antenna wires were short to the receivers and then the audio was sent down the sound snake to the House Mix position. The disadvantage to this is you can't see the display on the receiver, but the signal strength will be huge.

 

[TimmyP1955]

With that much distance from the xmit to rcv, I'd consider using the PWS/Shure Helical antennas.

If I could not budget UHFR, I'd go Sennheiser instead of Shure (plus Senny capsules sound better if you end up getting any handhelds). (I've not heard the high end Senny Vs UHFR - but there's the Senny capsules.......)

 

[mbenonis]

With that much distance from the xmit to rcv, I'd consider using the PWS/Shure Helical antennas.

If I could not budget UHFR, I'd go Sennheiser instead of Shure (plus Senny capsules sound better if you end up getting any handhelds). (I've not heard the high end Senny Vs UHFR - but there's the Senny capsules.......)

It's too bad those PWS helical antennas cost so much. You could probably build one for $30-40 from the hardware store...

 

[zuixro]

With that much distance from the xmit to rcv, I'd consider using the PWS/Shure Helical antennas.

If I could not budget UHFR, I'd go Sennheiser instead of Shure (plus Senny capsules sound better if you end up getting any handhelds). (I've not heard the high end Senny Vs UHFR - but there's the Senny capsules.......)

Which Sennheiser wireless do you recommend? I've always used Shure. At my other job, the only Sennheiser wireless we have is rental gear. All the production stuff is Shure.

 

[Chris15]

There is a train of thought that says EW Sennhesier is the way to go unless you are able to afford UHF-R. R series trumps most Sennheiser and indeed most of the other systems on the market. At a Price...

I have however had a colleague say that Sennheiser ONLY sounds good with the Neumann capsule. I don't disagree, but I also don't have the ears to comment...

 

[bishopthomas]

Which Sennheiser wireless do you recommend? I've always used Shure. At my other job, the only Sennheiser wireless we have is rental gear. All the production stuff is Shure.

I recommend going for the best that you can afford. In general, you pay for what you get. The higher end Sennheisers are more frequency agile. The 300 series and up allow connection to their wireless manager which is an amazing tool, especially for portable applications. I have also used the Shure UHF series and they are nice too, but not cheap. As far as Sennheiser/Shure goes, it's still a 58 (or whatever) capsule no matter how fancy the transmitter, so take that into consideration. For basic handheld applications I like the 835 (in the Sennheiser 100/300 series) much more than the 58 (Shure's standard capsule), so I choose Sennheiser. For lav mics (and unless they've changed the design with the introduction of the G3's) I really think the build quality of the stock Sennheiser mic is total junk. The plastic clip is crap and the element is huge and unsightly with that big mesh grill on it. It sounds decent, but looks ridiculous. You can upgrade the capsule, though, at a price.

Another thing to think about is distribution. I'm not sure how the prices compare for antenna distro. The Shures have Edison loop throughs and the Sennheisers get their power from the distro. I have a friend who is buliding a rack of Shure UHFR's right now. He's only doing it because he got a great deal, otherwise he would be expanding his rack of Sennheiser 300 series. He took his rack of ULX's to NYC a few weeks ago and litterally could find NO usable frequency. I mean, full Rx levels for every single channel. He had to rent UHFR's at the last minute. We took his Sennheiser 300 and my 500 the next gig, connected it to the PC-based wireless manager, scanned, and picked available frequencies from the plot. Worked perfectly all night.

 

[zuixro]

I recommend going for the best that you can afford. In general, you pay for what you get. The higher end Sennheisers are more frequency agile. The 300 series and up allow connection to their wireless manager which is an amazing tool, especially for portable applications. I have also used the Shure UHF series and they are nice too, but not cheap. As far as Sennheiser/Shure goes, it's still a 58 (or whatever) capsule no matter how fancy the transmitter, so take that into consideration. For basic handheld applications I like the 835 (in the Sennheiser 100/300 series) much more than the 58 (Shure's standard capsule), so I choose Sennheiser. For lav mics (and unless they've changed the design with the introduction of the G3's) I really think the build quality of the stock Sennheiser mic is total junk. The plastic clip is crap and the element is huge and unsightly with that big mesh grill on it. It sounds decent, but looks ridiculous. You can upgrade the capsule, though, at a price.

Another thing to think about is distribution. I'm not sure how the prices compare for antenna distro. The Shures have Edison loop throughs and the Sennheisers get their power from the distro. I have a friend who is buliding a rack of Shure UHFR's right now. He's only doing it because he got a great deal, otherwise he would be expanding his rack of Sennheiser 300 series. He took his rack of ULX's to NYC a few weeks ago and litterally could find NO usable frequency. I mean, full Rx levels for every single channel. He had to rent UHFR's at the last minute. We took his Sennheiser 300 and my 500 the next gig, connected it to the PC-based wireless manager, scanned, and picked available frequencies from the plot. Worked perfectly all night.

We already have our wireless mic elements, Shure WL93's. They have the little XLR looking connector (the name of which escapes me) (EDIT: Just found it in another thread, Lemo plug, I think), I don't remember what kind of connector the Sennheiser ones have. (I think I saw some with an 1/8" TRS, that would be a problem)

I included antenna distribution in the quote I gave to the TD. I got a quote from Full Compass for 4 dual receivers, 8 belt packs, 2 hand helds, 2 antennas, 1 distro, a road case, cable, etc, and it was gonna be like $16k. That might be a little difficult to swing...

 

[mbenonis]

We already have our wireless mic elements, Shure WL93's. They have the little XLR looking connector (the name of which escapes me) (EDIT: Just found it in another thread, Lemo plug, I think), I don't remember what kind of connector the Sennheiser ones have. (I think I saw some with an 1/8" TRS, that would be a problem)

Shure bodypacks use TA4F connectors, save for the old UHF stuff I believe. Sennheiser uses 1/8" connectors with a threaded sleeve for their Evolution series, and LEMO 4 pin for 3k/5k. Not sure about Sennheiser 2k.

I've used WL93's in the past, and they're okay mics. I prefer the Countryman B3 myself, which can be had for ~$150 terminated however you want.

I included antenna distribution in the quote I gave to the TD. I got a quote from Full Compass for 4 dual receivers, 8 belt packs, 2 hand helds, 2 antennas, 1 distro, a road case, cable, etc, and it was gonna be like $16k. That might be a little difficult to swing...

What line did you spec out? That seems a bit high to me to be Shure ULX or Sennheiser 300 series, but it does include all of the accessories... What antennas, coax, and distro did you spec? I'd hate to see you order something overpriced/unnecessary (many of the manufacturer antennas and almost all manufacturer coax falls into this category)

 

[zuixro]

Shure bodypacks use TA4F connectors, save for the old UHF stuff I believe. Sennheiser uses 1/8" connectors with a threaded sleeve for their Evolution series, and LEMO 4 pin for 3k/5k. Not sure about Sennheiser 2k.

I've used WL93's in the past, and they're okay mics. I prefer the Countryman B3 myself, which can be had for ~$150 terminated however you want.



What line did you spec out? That seems a bit high to me to be Shure ULX or Sennheiser 300 series, but it does include all of the accessories... What antennas, coax, and distro did you spec? I'd hate to see you order something overpriced/unnecessary (many of the manufacturer antennas and almost all manufacturer coax falls into this category)

Ah-ha! TA4F. I realized it wasn't LEMO after I looked at the wiki article. The WL93's are what came with our old wireless mic system, so I'm guessing we just bought more to keep them consistent.

$16k was for 8 channels of UHF-R. Here is what was in my quote:

4* Shure UR4D L3 Dual UHF-R Receiver 638-698 | Full Compass
8* Shure UR1 L3 UHF-R Wireless Bodypack Transmitter only, 638-698 | Full Compass
2* Shure UR2 SM58 L3 UHF-R Handheld transmitter with SM58 head 638-698 | Full Compass
2* Shure UA870USTV UHF Antenna,Wide Band 470-698 | Full Compass
2* Shure UA845SWB Antenna/Power Distribution System, 470-952 MHz | Full Compass
2* Shure UA825 25' UHF remote antenna extension cable, BNC to BNC | Full Compass
1* Grundorf Corp ML 12 12 RU Mighty Lightâ
2* TecNec TN RD2 2RU Rack Drawer with Key Lock | Full Compass
1* Pro Co RM0800FF 10 10 ft. 8 Mic Channel, No Returns Fan to Fan Snake | Full Compass

Actually, I think I added more to that after I got the $16k quote so it may be closer to $17k. I also got a ULX quote which was about $8.5k.

 

[mbenonis]

Skip the antenna. As stated above (I think), you do not want an active antenna. Get a passive one, like these:
Shure PA705 Antenna for Shure PSM Wireless Systems | Full Compass
Lectrosonics ALP500 Log Periodic Dipole Array (LPDA) Antenna, Shark Fin, For Fixed Applications | Full Compass

They're still a bit pricey but that's what you get for buying a turnkey product instead of building your own (which you could probably do for ~$50).

Also: that coax cable is costing way too much and is too lossy for your use anyway. Get something like LMR400 or LMR240 at the exact length you need (you'll need a pair, of course) terminated with BNC Connectors:

RF Connection Coaxial Cable

At their cost of $5 per connector plus $0.82 per foot (for LMR400, LMR240 is cheaper) you're looking at $30 MAX for a 25 foot run. And that's for a much much better coax cable.