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[Michael B. Miller]

I am an AV tech for a professional development center in Texas. I have far less experience with the Audio side of AV, and up until January, I had a coworker who knew far more about audio systems than I ever did, so he handled everything but the most mundane aspect of the job. (I know how to change channels and adjust the gain to keep the system from feeding back, but beyond that I'm pretty clueless.)

He left for a new job at the start of the year, leaving me a little over my head in the Audio system we have here in the building.

That brings me to my question. Recently we've been having an issue where our mic systems will randomly emit a loud burst of static. It happens in multiple rooms, and doesn't seem to follow any kind of pattern. The mic doesn't even need to be on or in use for the static to come through. The night janitor has complained about it scaring him when the building is empty.

Since neither changing the channel, nor changing the gain seem to fix this particular problem, I'm stumped. I'm hoping someone with more knowledge and experience than me can point me in the right direction to get rid of this issue. I can provide more details as needed, but as it stands I'm not even entirely sure what details would be helpful.

On a side note, I'm new to this forum, so if this question should really be in a different thread, please let me know and I'll move it.

[Benjamin Krumholz]

That brings me to my question. Recently we've been having an issue where our mic systems will randomly emit a loud burst of static. It happens in multiple rooms, and doesn't seem to follow any kind of pattern. The mic doesn't even need to be on or in use for the static to come through. The night janitor has complained about it scaring him when the building is empty.

What city and state are you operating in.. Also what frequency band is the microphone.. Does it happen to be a Sennheiser Evolution? I have had simmilar problem.. Based around antenna placement.. outside LM frequencies that will pop in and out at random times.. What kind of antenna are you using.. Try moving the antenna if possible.. Raise squelch if possible.
Ben

[Michael B. Miller]

What city and state are you operating in.. Also what frequency band is the microphone.. Does it happen to be a Sennheiser Evolution? I have had simmilar problem.. Based around antenna placement.. outside LM frequencies that will pop in and out at random times.. What kind of antenna are you using.. Try moving the antenna if possible.. Raise squelch if possible.
Ben

I'm in Arlington, Texas. We have about 6 Transmitter/Receiver pairs on at a time (with one "floater" set that gets used on an as-needed basis).

https://www.bhphotovideo.com/bnh/controller/home?O=&sku=813276&gclid=Cj0KEQiA5vXEBRChycOl36LPn5EBEiQAJV2-bD4m2n_b_pfTyFQ2iz0xIhHm5I9hBR1GI-AHKEdd8hEaAqG28P8HAQ&is=REG&ap=y&c3api=1876%2C52934714882%2C&Q=&A=details

That's a link to the exact model we use. The two boxes I have access to now are on 670.200 and 653.800. I can check others as rooms clear out.

The rooms that are the worst offenders have the receivers mounted in a cabinet with the Crestron equipment. I can move their antennae a little bit, but not much. I'm not entirely certain what "squelch" is, or how to adjust it, so I'll need a bit of help on that front.

Edit: Just realized I didn't answer your question about what kind of antennae I was using. They're just the little rabbit ear types that connect to the back of the receiver. Nothing fancy or special.

[Jerome Malsack]

User manual.   http://www.telex.com/binary/FMR500_User_Manual.pdf 

Squelch  on page 3  Number 10.

[Tim Steer]

Your radio mic receivers are always receiving radio signal of some sort, but they contain a 'squelch' circuit that mutes the audio when that signal falls below a certain threshold (i.e. when the transmitter is switched off or goes out of range). Sometimes radio interference is sufficiently powerful enough to lift the squelch, and a burst of unwanted noise is heard. For this reason, it is generally bad practice to leave radio mic channels open when the transmitter is switched off.

1. Keep radio mic channels muted on the desk when the mics are not in use
2. Consider changing any frequencies that are 'repeat offending'
3. Think about nearby possible sources of interference
4. If you are still having issues, raise the squelch setting on the receiver (page 3 of the manual http://www.telex.com/binary/FMR500_User_Manual.pdf)

[Michael B. Miller]

Your radio mic receivers are always receiving radio signal of some sort, but they contain a 'squelch' circuit that mutes the audio when that signal falls below a certain threshold (i.e. when the transmitter is switched off or goes out of range). Sometimes radio interference is sufficiently powerful enough to lift the squelch, and a burst of unwanted noise is heard. For this reason, it is generally bad practice to leave radio mic channels open when the transmitter is switched off.

1. Keep radio mic channels muted on the desk when the mics are not in use
2. Consider changing any frequencies that are 'repeat offending'
3. Think about nearby possible sources of interference
4. If you are still having issues, raise the squelch setting on the receiver (page 3 of the manual http://www.telex.com/binary/FMR500_User_Manual.pdf)

In regards to number 2 and 3, is there an easy way to determine which frequencies are prone to interference? Our building is in a pretty densely populated area, so I suspect there are a lot of sources of interference, not all of which would be in my control.

I'll adjust the squelch on the worst offenders, and see if that fixes the issue. Sounds like it should. I'll report back in a week or so with the results.

Thanks for the help.

[Michael B. Miller]

User manual.   http://www.telex.com/binary/FMR500_User_Manual.pdf 

Squelch  on page 3  Number 10.

I probably could've googled that myself, huh? I appreciate your making it easy for me.

[Tim Steer]

Change the frequency first and adjust the squelch as a last resort. It's better to find a channel that is free from interference, than to make do with a noisy channel and just whack the squelch setting up.

I'm not familiar with that Telex unit, but the manual suggests it has an autoscan function, which may be your first port of call when it comes to choosing the best channel. I'm not familiar with US licensing regs, but needless to say, keep it legal and don't use licensed channels unless you are paying for them.

[Michael B. Miller]

Change the frequency first and adjust the squelch as a last resort. It's better to find a channel that is free from interference, than to make do with a noisy channel and just whack the squelch setting up.

I'm not familiar with that Telex unit, but the manual suggests it has an autoscan function, which may be your first port of call when it comes to choosing the best channel. I'm not familiar with US licensing regs, but needless to say, keep it legal and don't use licensed channels unless you are paying for them.

On some of these boxes, I've changed the frequency dozens of times. I hadn't been using the auto scan, so I'll try that and see if it makes a difference.

Thanks for the advice.

[Mac Kerr]

On some of these boxes, I've changed the frequency dozens of times. I hadn't been using the auto scan, so I'll try that and see if it makes a difference.

Thanks for the advice.

DO NOT change the frequencies in a multi unit system without doing a frequency coordination to make sure the frequencies are compatible with each other!

The biggest problem you have is the antennas mounted inside racks. They need to have line of sight without obstructions from the antenna to the transmitter. If no previous coord has been done you should do that ASAP. If you cannot do that yourself with the free software from Shure or Sennheiser, list all your wireless equipment and the tuning band each uses here and someone will probably give you a list of good frequencies.

Mac

[Ike Zimbel]

I'm in Arlington, Texas. We have about 6 Transmitter/Receiver pairs on at a time (with one "floater" set that gets used on an as-needed basis).

The rooms that are the worst offenders have the receivers mounted in a cabinet with the Crestron equipment. I can move their antennae a little bit, but not much. I'm not entirely certain what "squelch" is, or how to adjust it, so I'll need a bit of help on that front.

Edit: Just realized I didn't answer your question about what kind of antennae I was using. They're just the little rabbit ear types that connect to the back of the receiver. Nothing fancy or special.

A couple of years ago I was called in to consult at a university facility that was having similar issues, and this was the biggest problem. Putting the antennas in the back of a metal rack, sometimes in a closet or room adjacent to where the mics are being used, is a real problem with AV installations. The receiver antennas need to be close to the transmitters. That said, it would be helpful to check your squelch settings and make sure they are not too low. It's possible, for example, that they come factory set to the lowest setting. But...keep in mind that raising the squelch level will reduce the sensitivity of the antennas, so if they are all ready struggling to receive the mics, this could make things worse.
And finally, If six identical units are all the wireless that you are using, the auto scan feature could help, but what you need to keep in mind is that you will have to do the scan on one unit and then transfer the results to the other units (IOW, you shouldn't do the scan on each unit). So, scan on on unit. It will find the Group with the most available channels, say, Group-1. Save the first available channel on that unit, and then make a list of the rest of the available channels and program one of those manually into each successive unit.

[ProSoundWeb Community]