Wireless At A Loss with Shure SLX Drop-out

[insano768]

Hello...this is my first post here. I've enjoyed reading posts here!

This is a church application. I have 8 Shure SLX systems (4 H5, 4 L4) and I've recently re-mounted them FOH. I'll explain that below, but I've let me continue explaining the set-up. I have 2 Shure 844 distribution sytems, and they are combined with a Shure UA 221 combiners, and 2 Shure PA SWB805 LDP antennas.

OK! So I could not get rid of ground loops on 4 of the systems when they were mounted stage side which drove me crazy. I never had any dropout issues. I was even running 1/4 antennas that shouldn't have worked, but they did. So due to the annoying buzzing, I moved all 8 systems and distribution to FOH. This solved the ground loop issue as the buzzes are gone. The plan was to remote the antennas no more than 30ft mounted to a wall using some decent RG-6. FOH/Wall is propbably no more than 90ft from the stage. So in theory, I'm thinking I should be good. Yesterday, I hadn't mounted the LDPs yet, and had them on mic stands elevated pretty good. And Shure (I mean sure!) enough I had bad drop-out issues for 3 services. Awesome!

So what do I do. Tonight I will run the Shure Wireless Workbench software to get a frequency plan, because quite honestly, I've never really done this properly. With a 15ft shot before, it probably wasn't near an issue as it is now. The other thought was to to remote the antennas back up to stage side. But then with going up through the ceiling and back down, this is probably a good 150ft. Would I have detrimental loss? I want to stay away from amplifiers as much as possible, but I'm guessing with the R6-6 I have at 150ft, it just might be stretching a bit far.

So I need help! What are your thoughts. I'm also gonna call the great folks at Shure. They really are helpful! I mean that!

Thanks again.

 

[Dillon]

Here's a real quick response... I've only got a couple minutes:
*Leave the receivers at FOH if that eliminates all buzzes, hums and things that go bump in the night.
*Try to solve the drop-out for ONE transmitter at first. Power it up, set it up out on stage (or at the lectern, choir position, etc) where you are having dropout troubles.
*Look at the receiver and watch how changing the position and orientation of the antenna paddles from FOH affects the RF reception strength. Make sure you are getting good diversity between the two antennas. Try unplugging each antenna individually to make sure the other one is functioning fine. If you see one side receiving stronger than the other, swap the antennas to make sure your distro/combiners are properly patched.
*Check your antennas and distros for any sort of gain adjustment -- I don't know these models very well.
*Dropouts and intermod are two different animals altogether. Running Wireless Workbench is a good idea to coordinate your RF system and mitigate intermod between channels, but it will not likely solve any dropout problems.
*Keep the antenna runs short. You should be fine running two cables at 25-30 ft. You shouldn't have a problem hitting the transmitters from 90 ft away.
*Remember: keep the troubleshooting SYSTEMATIC. Work through it one step at a time.

Good luck.

 

[metti]

One possible solution would be to figure out a way to make sure that they are connected to the same circuit as FOH. You could put them back at their old side stage position and then just run a power cable to them from FOH. A normal 12/3 could easily go 150' and this would almost definitely fix your ground loop.

 

[mbenonis]

Good advice so far, and especially a good game plan on your end. Read my guides on wireless mics and the stuff on my website too; that'll help. I know it's poorly organized but there's some good stuff there.

Once you coordinate your frequencies (and make sure that you're not on top of any high power TV stations), come on back and let us know how things are working.

 

[insano768]

OK. So I have set frequencies per Shure's guidance. I'll keep you all posted. Another idea I just had...I just had new circuits installed for speakers in the ceiling. I am thinking about trying to run power from there back behind stage...30 ft or so. Then I could get my antennas back stage side. And pull my power from a different circuit. If this eliminates and ground loops, this may be the way I go.

 

[FMEng]

OK. So I have set frequencies per Shure's guidance. I'll keep you all posted. Another idea I just had...I just had new circuits installed for speakers in the ceiling. I am thinking about trying to run power from there back behind stage...30 ft or so. Then I could get my antennas back stage side. And pull my power from a different circuit. If this eliminates and ground loops, this may be the way I go.

Since the audio circuits are balanced, the simple way to break the ground loop is to open the shield at the connector plugged into the receiver. Make sure the shield is trimmed and insulated (heat shrink is good) from the connector shell and pin 1. The shield should only be grounded at one end in this situation.

Do this instead of messing with with the AC power ground.

 

[insano768]

UPDATE: I made some group/channel changes per the freq plan I got from Shure. I ran 5 services with 250+ people per and had no issues at all. Running as many as 6 systems at a time. So I'm hoping I can move on to the next great hurdle. Tuning the room properly! Thanks for all your help.

 

[gcpsoundlight]

RG-6? Make sure the impedance is matched... IE, use RG-6 if it is 75ohm, or RG-8 if it is 50 ohm

 

[Chris15]

RG-6? Make sure the impedance is matched... IE, use RG-6 if it is 75ohm, or RG-8 if it is 50 ohm

Please go back and read the vast range of information here that comes to the conclusion that in many cases, better performance will be derived from using 75R coax not 50R. IEM transmission will NEVER be one of those cases, but most passive reception is.

 

[Call911]

I would definitely urge you to double and triple check your freqs. I recently ran a community theater musical of Annie with 24 SLX mics, 12 J3 and 12 H5. We had zero issues at all. In my area I have had great luck with literally setting the channels all on 1, and just doing 1-1, 1-2, 1-3, etc. on both the J3 and H5 freqs. We had 1 problem, and I changed the frequency to channel 2 and it was instantly fixed.

Keep in mind we ran the wireless mics FOH at the board, about 75' from the stage. We use 1/2 wave antennas, with a set of 4 mics ran into an antenna distro.

It's a fantastic system, the Shure SLX have worked wonders for my school district. A good system at about $500 a mic.

 

[mbenonis]

The idea behind Shure's groups and channels is that you can do exactly that: set it to 1-1, 1-2, 1-3... and have it work as long as there is no TV channels in use for TV. The groups are pre-selected to be third-order intermodulation clean.

The SLX mics are OK for their price in my opinion, but as I recall they do poorly in congested RF encironments. If you're in a rural area they're probably fine though!

BTW, I think its covered in my guide, but RG-6 is absolutely fine for receive and cost-wise is much more cost-effective than RG-8. If you need runs longer than a few tens of feet though I might look at RG-8 (like Belden 9913 or equivalent) or even Times Microwave LMR-400 or similar.

Handy table:
Coax Attenuation Chart
Use the 700 MHz figure as a worst-case scenario for WM use.

Mike