Wireless Mic Trouble

[2mojo2]

We recently installed 12 Shure SLX lav sets.
I put six receivers in each of two custom cabinets with rack rails.
Each cabinet has a heavy steel back with 12 antennas spaced out. These are connected by short supplied coax cables to the receivers.
Each cabinet is placed in a wing, right up of the proscenium wall. No part of the stage is more than 50 or 60 feet from the receiver.

I am getting drop-outs. I can see the carrier signal reception going in and out.

We are using the automatic frequency programming procedure. I trust that the built-in program is not making poor frequency choices, but I don't know.

I realize that I cheaped out with the antenna approach. If central antennas and distribution amps will make all the difference, I can start lobbying for those. What I can't do is spend thousands on top of thousands already spent and end up with the same problem.

Ideas?

[avkid]

Are the antennas inside the racks?

[waynehoskins]

... and if not, is the steel rack between the receiving antennas and the transmitters? (line-of-sight, or lack of it)

[museav]

How are the antennas mounted, do you have them organized in any way? What kid of spacing is there between the two antennas for a receiver? Are the antennas angled so that they are at 45 degrees with the two antennas for a receiver are perpendicular to one another? When you set the frequencies, did you have all the other mics on?

You might first try determining in the drop outs happen with just one receiver operating. Pick the one system that seems to be worst and turn off all the other transmitters and receivers, do you still get drop outs?

Are all your units in the same operating band? Shure says that you can get "up to" 12 SLX systems in a single band but that does not necessarily mean you will actually be able to get 12 working together. Any other RF sources in that band or any of a number of issues and it might be less than 12.

A few other points. The antennas should stick out above the racks, if some antennas are entirely behind the rack that could be a problem. The antennas also need to be grounded, each antenna should get its ground via the connector shell to the chassis mount connector that should then be grounded to the rack panel that should be grounded to the rack and then that to ground. If you have something like the metal panel mounted in a wood or plastic rack, the panel isolated from the rack or nothing grounding the rack then that might be a problem.

[DaveySimps]

I second the aforementioned thoughts about antennas. We run 12 of the SLX on the H5 set and another 8 on the J3 set and have had no issues with them at all. But lady RF can be a cruel mistress, and plague many locations with horrible problems. How are the channels you are running on coordinated? The auto select function is a nice feature, but with that many units running, proper frequency selection is much more reliable. Shure's Wireless workbench software is available on their site, and is a great resource to help you in that department.

Shure - Wireless Systems - Wireless Workbench 5.0.1 Software

~Dave

[2mojo2]

We are running four units on G4, four on G5, and four on H5.
The antennas are exterior to the plate, with the BNC connectors grounding the plate.
There are three rows of four, spaced four inches on center vertically.
The two antennas connected to any unit are separated eight inches horizontally.

Tech Assistance at Shure ran the Wireless Workbench software for me and sent a schedule of frequencies. We programmed the receivers, synced the transmitters, and tonight's show ran pretty well.

I had a few noises, but these may have been attributable to actors bumping the mics.
Huzzah! to Shure for the timely assistance.

[Chris15]

I don't think we resolved the antenna orientation... From what I'm reading you have 2 cabinets, 6 receivers in each and 12 antennas mounted on the back panel of each cabinet. So presuming that each row of antennas feeds 2 receivers, we have something like this:
\(a) \(b) /(a) /(b)
where a and b refer to the 2 receivers.

As noted by others, you want 45 degree orientation on those antennas.

I can't find G4 and G5 bands for SLX on the Shure website...
H5 has a low frequency of 518 MHz, which correlates to a wavelength of 579mm. I'm trying to remember, but rule of thumb is to try and get diversity antennas at least a wavelength apart where possible. Your 8 inch spacing represents less than have a wavelength of separation.

I tend to think that probably you would get better performance from antenna distribution. In that event, you might be better off with all the receivers in one rack - you then need only 3 distros. External antennas, probably log periodic dipole arrays would be directional and could be better spaced for diversity.

[2mojo2]

Shure's literature indicates that the minimum spacing of the two antennas for a receiver is 1/4 wavelength, or about 4 inches for a UHF unit. They go on to say that more distance is desirable, but that anything over one wavelength is pointless.
Taking this info and available space into account, I arrived at 8 inches, about one half wavelength. Layout is as shown. Vertical distance between rows is about 5 inches.

\(a) \(b) /(a) /(b)

\(c)\(d) /(c)/(d)

\(e)\(f) /(e)/(f)

On of the reasons I set this up in two cabinets is the 6 mic sends available in each wing. In addition, the small cabinets can be locked up in available space when not in use.
In the long run, I may find an antenna disto arrangement necessary.
As it stands, I tried to tailor the installation to the space, wiring, money, and property needs of the group.