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Author Topic: Need Help / Suggestions For IEM RF Issues  (Read 32435 times)

Terry Martin

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Need Help / Suggestions For IEM RF Issues
« on: February 14, 2017, 11:33:23 AM »

I've started a new topic for clarity - the original located here....
http://forums.prosoundweb.com/index.php/topic,161853.msg1492448.html#msg1492448

The original topic has become much less of an issue, as I'm now dealing with RF issues.   ...which I thought were related to a new equipment purchase (X32 Rack).

The situation (for those that weren't following) is that I am dealing with random RF interference (swooshes, spikes, etc) in the IEM system.  All packs exhibit the problem.

Gear:
(4) Sennheiser G2 IEMs / 518~554 MHz (A Band) / AC2 Combiner (have both 1/4 antenna and Omni antenna)

I had received some feedback from Kevin Maxwell about coordinating the frequencies - thank you very much!  Unfortunately, that did not fix the problem.  Based on my assessment of the available frequencies in my area, I'm almost to the conclusion that enough frequencies in my area have been sold off to render the equipment (almost) unusable.   (http://sennheiser.us/freqfinder/index2.html)

We are located in/around zip 47711, but travel to 62839, 62450, 40108, 42420, 47460, 47421 regularly (basically Western Kentucky, Southern Illinois, Southern Indiana).  We have a large venue in Evansville, IN (Ford Center - 11,000 capacity) - how do you touring RF Coordinators handle this area?  Do you not have A Band gear?

If someone would be so kind to give me some advice, I would really appreciate it.  I am no RF expert, but I've done a ton of reading over the past couple of months.  This problem just started happening in December as we purchased the X32 Rack - the IEMs were being used prior to that with an A&H Mix Wiz (trouble free).  Is it a coincidence that the RF problems started right when we made the switch??  This condition also happens whether I'm using 1/4 wave or Omni antenna.

So, my real question is should I try and sell off the A Band G2 gear and purchase G3 gear in the G Range (566-608 MHz)?  This has been very frustrating.  Thank you in advance.
« Last Edit: February 14, 2017, 11:37:08 AM by Terry Martin »
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John Sulek

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #1 on: February 14, 2017, 11:50:44 AM »

Are you sure that the bnc cable you are using for your iem antenna is 100%?
I didn't see this mentioned in your original thread, and it would account for less than solid performance. Look carefully at the center pin and make sure it is not loose or pushed back into the connector body. Check the cable for sharp bend or kinks.
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Terry Martin

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #2 on: February 14, 2017, 12:16:42 PM »

Are you sure that the bnc cable you are using for your iem antenna is 100%?
I didn't see this mentioned in your original thread, and it would account for less than solid performance. Look carefully at the center pin and make sure it is not loose or pushed back into the connector body. Check the cable for sharp bend or kinks.

No, I'm not. But will check that tonight.


Sent from my iPhone using Tapatalk
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Tim McCulloch

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #3 on: February 14, 2017, 01:39:34 PM »

Terry, that this problem follows you around is what "gets" me and I fully understand why you think the X32R could somehow be involved.  Post hoc, ergo proptor hoc (after this, therefore because of this - it's a "logical fallacy" though).

You did a bunch of other stuff when you added the X32 (patch wiring, antenna wiring, mounting, powering, etc) and this could be the result of a *combination* of factors that will defy simple troubleshooting (like you don't know that already :( )

Does this happen at every performance (or nearly every performance)?  Have you been able to duplicate the failure at home?  The last question is important because the problem seems to follow you around - if you can't duplicate it without the band playing, with the lights running etc, then I'm highly suspect of something the band owns or uses that spews RF but is not a wireless system transmitter and that is not present when you set the rig back up at home.

Another possibility is that this is an INPUT side issue with a wireless hand held or instrument system receiving the interference hit and it's being propagated thru the IEMs as part of the audio mixes.  Since everyone in the band probably gets the lead vocal or lead guitar in his/her mix, everyone would experience it to the degree that source is in each mix.  With wireless receivers for the mics/instrument packs it's easier to see RF hits on the signal meters but an IEM pack gives very little visual indication of what is happening and it's the audio that tells the user there is a problem.

If you're able to duplicate this at home, try removing the X32R from the rack and get it a couple of feet or more from the rest of the kit.  If the problem goes away there possibly is some RF leakage from the mixer.  We see lots of band IEM rigs built much like yours with the same products and have not heard anyone blame their X32R, but that doesn't mean yours is okay.  IF the problem does not go away I'd be looking at the integrity of the RF path from transmitters to combiner and from the combiner to the paddle/helical/whatever.

There was a recent comment here about a bad SDI cable termination that spewed RF and I think I had a very similar problem a couple months ago.  At the tech island I had the half of the wireless mic receivers (for presenter lavs) but had the receivers for the hand-held mics back stage by the snake head.  I had problems with drop outs on lavs regardless of what frequency groups or individual frequencies were selected.  I started with a scan without any transmitters on and let the Shure receivers find the group, then turned on each transmitter and let the receiver scan again... repeat until done.  It all worked until the event started.  What changed?  More and more video stuff was being brought on line.  I've done this event before with the same video crew but they brought all brand new stuff this year, including a bunch of SDI/HDMI conversion that we'd not used before.  The HH wireless receivers were rock solid, and they were in the same frequency group as the lav packs.  The difference?  The HH receivers were 75 feet from FOH tech island.  This contributes to my suspicion that something on stage is spewing broadband RF in your situation.
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Terry Martin

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #4 on: February 14, 2017, 03:01:07 PM »

Hi, Tim.  Thank you for the details.  I will do my best to respond to your points/questions....

Yes, this problem does follow us around.  It seems to happen at every venue, however sometime much worse (i.e. more impactful to our performance) than others.

I can duplicate the situation at home.  Its very weird to me.  I can walk all around the room, and it will only occur in one spot, holding the receiver in just the right angle, etc.  It's not interfering 100% of the time - only on occasion, very random - but when it spikes, it is slightly painful if the pack is at "concert" level (generally 6-7 on the pack).

So last night, I did more testing.  First I confirmed that I could duplicate the problem with the rack powered up.  ...X32 Rack on, Wifi Router on, IEMs on, Combiner on.  Check I could duplicate as described above.
Next, I turned off the X32 Rack (and unplugged it).  I could still duplicate the problem.  There should be no RF leakage if the unit is not powered up right?
Next, I turned off the wifi router (and unplugged it).  I could still duplicate the problem.  There should be no RF leakage if the unit is not powered up right?
I also disconnected the XLR jumpers that connect the X32 Rack to the individual IEM transmitters.  I could still duplicate the problem.
I re-ran WWB and input newly coordinated frequencies.  I could still duplicate the problem.
When I re-ran WWB,  I had it spit out back up frequencies, so I input the those.  I could still duplicate the problem.
I did an auto scan on the IEM receivers themselves and changed all of the transmitters.  I could still duplicate the problem.
A few weeks ago, I removed the combiner and ran each transmitter off of its own power and 1/4 wave antennas, problem was still there (although I was in a different location/ not at home).

Input side issue has been confirmed.  As last night, I didn't have any inputs to the X32, and additionally I had XLR jumpers disconnected from the transmitters.

When I get the interference, I do see the RF meters on the packs backoff a few bars.

I've been asking around to see if someone locally has an RF Analyzer, but I haven't located anyone yet.  Not sure what that will tell me, but it might help if it was in the right hands.

Thanks again Tim.
Terry



Terry, that this problem follows you around is what "gets" me and I fully understand why you think the X32R could somehow be involved.  Post hoc, ergo proptor hoc (after this, therefore because of this - it's a "logical fallacy" though).

You did a bunch of other stuff when you added the X32 (patch wiring, antenna wiring, mounting, powering, etc) and this could be the result of a *combination* of factors that will defy simple troubleshooting (like you don't know that already :( )

Does this happen at every performance (or nearly every performance)?  Have you been able to duplicate the failure at home?  The last question is important because the problem seems to follow you around - if you can't duplicate it without the band playing, with the lights running etc, then I'm highly suspect of something the band owns or uses that spews RF but is not a wireless system transmitter and that is not present when you set the rig back up at home.

Another possibility is that this is an INPUT side issue with a wireless hand held or instrument system receiving the interference hit and it's being propagated thru the IEMs as part of the audio mixes.  Since everyone in the band probably gets the lead vocal or lead guitar in his/her mix, everyone would experience it to the degree that source is in each mix.  With wireless receivers for the mics/instrument packs it's easier to see RF hits on the signal meters but an IEM pack gives very little visual indication of what is happening and it's the audio that tells the user there is a problem.

If you're able to duplicate this at home, try removing the X32R from the rack and get it a couple of feet or more from the rest of the kit.  If the problem goes away there possibly is some RF leakage from the mixer.  We see lots of band IEM rigs built much like yours with the same products and have not heard anyone blame their X32R, but that doesn't mean yours is okay.  IF the problem does not go away I'd be looking at the integrity of the RF path from transmitters to combiner and from the combiner to the paddle/helical/whatever.

There was a recent comment here about a bad SDI cable termination that spewed RF and I think I had a very similar problem a couple months ago.  At the tech island I had the half of the wireless mic receivers (for presenter lavs) but had the receivers for the hand-held mics back stage by the snake head.  I had problems with drop outs on lavs regardless of what frequency groups or individual frequencies were selected.  I started with a scan without any transmitters on and let the Shure receivers find the group, then turned on each transmitter and let the receiver scan again... repeat until done.  It all worked until the event started.  What changed?  More and more video stuff was being brought on line.  I've done this event before with the same video crew but they brought all brand new stuff this year, including a bunch of SDI/HDMI conversion that we'd not used before.  The HH wireless receivers were rock solid, and they were in the same frequency group as the lav packs.  The difference?  The HH receivers were 75 feet from FOH tech island.  This contributes to my suspicion that something on stage is spewing broadband RF in your situation.
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Tim McCulloch

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #5 on: February 14, 2017, 03:22:40 PM »


I can duplicate the situation at home.  Its very weird to me.  I can walk all around the room, and it will only occur in one spot, holding the receiver in just the right angle, etc.  It's not interfering 100% of the time - only on occasion, very random - but when it spikes, it is slightly painful if the pack is at "concert" level (generally 6-7 on the pack).

Receiver, as in one unit?  Just 1 pack?  Or is this consistent with every receiver?

Without the combiner, without any other obvious source of RF I'm running out of speculation.
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Terry Martin

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #6 on: February 14, 2017, 03:23:56 PM »

Sorry, I can duplicate on all packs.

Receiver, as in one unit?  Just 1 pack?
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Tim McCulloch

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #7 on: February 14, 2017, 03:25:22 PM »

Sorry, I can duplicate on all packs.

The common element to all this is you.  I think you're actually a spark-gap transmitter disguised as a human being. /satire

Seriously, with the transmitters on individual antennae, with no inputs connect to the transmitters and using "apparently good" frequencies and grouping there is some source of broadband RF and right now your body (or your personal electronic devices) are the common thread.
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Terry Martin

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #8 on: February 14, 2017, 03:40:44 PM »

I thought about that - I did get a new gold crown in December!  LOL  But in all seriousness, all band members are hearing the interference when we are on stage.  Generally speaking, when the band is at full tilt, there is no noticeable interference.  But between songs, we occasionally get the RF hits.

I had our band sound engineer with me last night as we were doing testing - he could duplicate the condition as well, with a different pack - at the same time that I was picking up the RF (with a different pack).   

...and currently, the transmitters are not on different antenna's - but I did do a trial with that arrangement a few weeks ago. 

The common element to all this is you.  I think you're actually a spark-gap transmitter disguised as a human being. /satire

Seriously, with the transmitters on individual antennae, with no inputs connect to the transmitters and using "apparently good" frequencies and grouping there is some source of broadband RF and right now your body (or your personal electronic devices) are the common thread.
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Tim McCulloch

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Re: Need Help / Suggestions For IEM RF Issues
« Reply #9 on: February 14, 2017, 03:58:53 PM »

I thought about that - I did get a new gold crown in December!  LOL  But in all seriousness, all band members are hearing the interference when we are on stage.  Generally speaking, when the band is at full tilt, there is no noticeable interference.  But between songs, we occasionally get the RF hits.

I had our band sound engineer with me last night as we were doing testing - he could duplicate the condition as well, with a different pack - at the same time that I was picking up the RF (with a different pack).   

...and currently, the transmitters are not on different antenna's - but I did do a trial with that arrangement a few weeks ago.

If you got the same result with separate antennae, that pretty much eliminates the combiner itself.

Here's the deal, Terry.  With the amount of RF field strength from your IEM transmitters whatever is causing the hit has to be a relatively strong signal.  I'm beginning to think (scary!) you might have a bad transmitter.  Do you still get hits with only one transmitter on at a time (but with all the receiver packs on)?
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ProSoundWeb Community

Re: Need Help / Suggestions For IEM RF Issues
« Reply #9 on: February 14, 2017, 03:58:53 PM »


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