better antenna's for sennheiser wireless

[Mark Blasco]

We are running several sennheiser wireless mic systems (I believe they are the evolution 300's, but I would have to double check - they cost us about 1000 each with the handheld and lapel mics). We are having problems with dropouts. Some of our rooms are rather large, so the wireless mics can be fairly far away from the transmitters. Are there any replacement antennas that work better than the small telescoping ones that come with the kits? We don't have them rack mounted, so i would prefer something that can either attach directly to the back or has it's own stand. Is this a losing battle? Any suggestion is appreciated.

[agedhorse]

The obvious solution would be to locate them at the stage area. That's also the most common in pro touring applications.

[Mark Blasco]

We usually have the receivers at the stage. The issue is that we have multiple large rooms (we are a University Student Union Building), and we have groups that want to walk around the ballroom. We have yet to find a good solution to get a clear signal throughout the room.

[Scodiddly]

The next step is usually a directional "paddle" antenna and an "antenna distribution unit" to split the signal from one antenna to several receivers.

 

One thing to try is just to put a little space between the receivers - don't stack them up, but put them maybe a foot apart on a table. When you have several antennas very close together they don't work as well.

[Ear Abuser]

any antenna that has more gain will be more directional, so trying to cover everywhere will tough.

You might try to get the recievers up as high as possible, to try and get a line of sight path from the antenna , which will have the lowest signal loss.

 

You might also want to see if there is any significant signal that may be interfering. Get some of those EE students to drag a spectrum analyzer down there and see what's going on.

[agedhorse]

A directional antenna is only better in the desired direction and WORSE everywhere else. That's where the "gain" comes from.

 

For this application, an extended groundplane (maybe a 1/2-wave) up over people's heads would give better performance. An amplified ground plane antenna would be better... but there's increased liklihood for additional interference. Also, they can overload if you get the transmitter too close.

 

Karl would be the best one to answer these questions though.... it's his "day job" stuff;)

[where02190]

Get an antenna distribution system, so multiple receivers share a high powered antenna system.

 

Put the receivers onstage.

 

Get the antennas as high up as possible.

 

Get an RF frequency coordinator to properly tune your transmitters to prevent intermodulation and hetrodyning, a major cause of dropouts in multiple RF systems.

[bassred]

Amen, Distribution Antenna with receivers at stage area would be my opinion as well!

[agedhorse]

 

Originally posted by bassred Amen, Distribution Antenna with receivers at stage area would be my opinion as well!

 

It's an antenna distribution RF amplifier which is only a very small part of the equation. You still need an antenna, and ground plane or log-periodic are the two most common styles used depending on the pick-up gain pattern needed.

[where02190]

An antenna distro and getting the antennas above the band will solve your issues.

[karlw]

The starting place, as mentioned above, is to select the frequencies carefully. Then, you want to have antennas distributed properly. Dipole antennas are probably what you want, as they have a small amount of lateral gain while rejecting singnals from above and below. Then, they should be placed in the center of your operating area to minimize the distance between transmitters and antennas. Then, the placement should be as "line of sight" as possible, with as few obstacles in the way as you can manage. Someone else mentioned raising them up and this is a good suggestion, thus avoiding the signal traveling through big bags of water (people). Then you want the best possible cables (50 Ohm) to go between your antennas and your receivers. If using multiple antennas, or multiple receivers off a set of antennas, then you'll need an RF distro.

 

You may need to add RF amplifiers to boost the signal before pushing it through the cable and the passive distro box. Place the RF antennas BEFORE the cables.

 

Hope this helps.

 

-Karl

[where02190]

 

Then, they should be placed in the center of your operating area to minimize the distance between transmitters and antennas.

 

 

Actually you want split the antennas either upstage/downstage or SL/SR.

[agedhorse]

Karl - would you kindly describe the general patterns of the various antenna options and where each antenna type would be indicated as a better solution? Also, how does efficiency differ with 1/4-wave versus 1/2-wave and what are the tradeoffs to the longer wavelength multiples?

 

 

This is an informational area that is sorely overlooked when specifying receiver antennas IMO.

[karlw]

 

Originally posted by where02190 Actually you want split the antennas either upstage/downstage or SL/SR.

 

 

Good point - you do need to have some distance between your antennas for optimal diversity. Anything more than one full wavelength should do it, but I think your point is to have the antennas on the outside edge of the operating area. This way, as the transmitters move away from the center, they are always moving towards one antenna or the other.

 

My point was based on the OP's description that there were multiple areas used, thus, the overall antenna placement should be a "middle ground" between these areas, thus the transmitters would never be further than the radius of the overall area from the antennas. Both approaches can work, and it depends on the overall shape of the area.

 

Agedhorse - I'll do my best to answer your questions because they are good ones.

 

The various antenna patterns are roughly as follows:

 

1. Ground plane, also whip - generally an omni pattern but with the weakest pickup along the axial points (ends) of the antenna itself. Somewhat of a "doughnut" pickup pattern. These are a cheap, effective and easy antenna to use, and thus are the standard for typical receivers out of the box. These need to be tuned to length (generally 1/4 wave) to be most efficient.

 

2. True dipole antennas are slightly better than whip antennas thus rejecting more from the tip axis and picking up slightly more from the lateral axis. These are pretty close to the ideal antenna when you aren't looking for pronounced gain in one direction. For instance, they work well on a stage where the performers are moving around quite a bit. These also need to be tuned to length (1/4 wave) to be most efficient.

 

3. LPDA (Log-periodic dipole array) takes the dipole concept and adds an array at various lengths in a pattern. Typically "shark-fin" or "paddle" antennas are of this type, and they are offered by a number of manufacturers. These provide +4 to +6dB of gain in the frontal direction, and some attenuation to the rear. They are least sensitive from the top and bottom. These are wide-band antennas and thus do not need to be tuned specifically for a given range of frequencies. They are helpful when your performers move only within a given area, such as the front and center of a stage, etc. The pattern is like a cardioid microphone in the lateral plane, so there is quite a bit of forgiveness, at least to the front. But it is not adviseable to use these when the transmitters may end up behind such receiver antennas.

 

4. Yagi are even more directional, and are not often seen in this type of application. They look similar to LPDA, but use a different type of array.

 

I'm not familiar enough with the differences between 1/4 and 1/2 wave antennas in terms of efficiency differences. However, hardly anyone is using 1/2 wave stuff, mainly because of the size. And, antenna efficiency is more of an issue with the transmitters than the receivers in terms of tuning for length. Reciever antennas are fairly forgiving, while transmitters don't radiate nearly as well when the antenna is the wrong length.

 

Hope this helps!

 

-Karl

[agedhorse]

Thank you.

[ATOMICDOG1]

How about helical antenna with a distribiution system?

 

http://ratsound.com/ratsales/helical.htm

[rocksld]

I've got the Sennheiser IEM (evolution) 300 also. What I did to minimized dropouts was get a BNC ended Cable, connect it to the back and then connect my antenna to the other end and then hang it in the air on the back of the stage so that I improved my antenna line of site---never had any problems, I also ran a shure wireless guitar sys in my rack with no conflicts between the two

 

Rocksld

[6Imzadi]

 

Originally posted by Mark Blasco We are running several sennheiser wireless mic systems (I believe they are the evolution 300's, but I would have to double check - they cost us about 1000 each with the handheld and lapel mics). We are having problems with dropouts. Some of our rooms are rather large, so the wireless mics can be fairly far away from the transmitters. Are there any replacement antennas that work better than the small telescoping ones that come with the kits? We don't have them rack mounted, so i would prefer something that can either attach directly to the back or has it's own stand. Is this a losing battle? Any suggestion is appreciated.

 

 

I have done New Years Eve shows in the grand ballroom of the Sheridan here. The stage was on the north wall, and the sound riser was on the south wall. To get the snake from A to B, I had to go overhead. In the track of the faux wall.

Point being, if you were to attach the remote antenne to the center of the room and run your cable to the receivers, would this help in the dropout department?

A little outside the box, I know.

[karlw]

 

Originally posted by 6Imzadi if you were to attach the remote antenne to the center of the room and run your cable to the receivers, would this help in the dropout department? A little outside the box, I know.

 

 

The thing to watch for is that coax cable has losses. The better (read: more expensive) cable like Belden 9917 has very little loss, but it is thick, delicate, and difficult to work with. The range of loss in dB per 100 ft of cable goes from say 3dB per 100 ft (9913) to 27dB (!) per foot for RG174. This is in the middle of the UHF range at 700MHz. The higher the frequency, the greater the loss per ft.

 

So the answer is: it depends. If you have a long run and have some OK but not great cable (say, 12dB per 100ft) you will need an RF amplifier to boost the signal before you shove it down the cable. However, 12dB is about all you can get out of an RF amp, so, 100ft would be the max length of that cable you could use before you start incurring a net loss.

 

-Karl

[where02190]

 

Originally posted by 6Imzadi I have done New Years Eve shows in the grand ballroom of the Sheridan here. The stage was on the north wall, and the sound riser was on the south wall. To get the snake from A to B, I had to go overhead. In the track of the faux wall. Point being, if you were to attach the remote antenne to the center of the room and run your cable to the receivers, would this help in the dropout department? A little outside the box, I know.

 

 

Better yet, put the receivers in the air, keep the antenna cable short as possible, and run a subsnake to the receivers. XLR can run hundreds of feet with no audible loss, but every foot of antenna cable adds to potential reception issues.

 

This is a very typical setup for corporate events in ballrooms, where coverage over a large area is necessary, and for arenas and stadiums where the transmitter travels around the venue, such as concerts and sporting events.

[Scodiddly]

I would make the effort to use higher-quality coax (ideally RG-8, but it's thick and expensive) and to get the antennae out of racks and up high. Keeping the receivers close to the antennae is good, though may pose other problems - if you've got a transmitter battery meter display on the receiver, you definitely want it where somebody can keep an eye on it.

[where02190]

Yea it's not always feasable, and if you cannot get opportunites to change batteries every 3-4 hours(depending on what you're using for gear, so e are more efficient than others), then you really got issues.