Wireless mic. Signal interference or what?

T

The Plumber

New member
Hey, this post is on a somewhat complex sound situation. I'd really love to get the live sound recording experts' opinion here.

I'm videotaping a live talk event and I get constant interference on all frequencies (tried 4 or 5 different frequencies). The sound set up is as follows: the participants use two wireless handheld mics that send the signal to a reciever (these mic are in the 900Mhz range). I'm getting the signal from that wireless microphone receiver with a sennheiser evolution 100 g2 (A series 518-554Mhz) wireless system. The handheld mics work fine and send good sound to the speakers (thru an additional amplifier) but my signal is very unstable and drops constantly.

The only reason for this problem I can think of is that the handheld mics receiver is connected to an ungrounded electric socket (i figured that out because I got shocked when I touched my transmitter that is connected to that receiver).

If you've read thru this and understood what I'm talking about you probably deserve a nobel prize. God bless you for your effort.

Thanks!!
 
So you are saying that you are taking the audio from the handheld receiver and then feeding it through ANOTHER wireless link?
Presumably you have a REALLY REALLY good reason for doing this.
 
I assume the wireless mic receiver is really a dual-channel unit with independent receivers (and most likely antennas) for the two mics, right? I mean, you're not trying to receive two mics with one receiver (a recipe for disaster)?

What is the distance from your G2 transmitter to receiver? What part of the world are you located in? Is this a city with lots of broadcasters, public-service radio and other RF sources around? Have you set the level controls on your G2 transmitter appropriately for the system you're feeding into it (mic or line level)? Oh, and are we talking about the belt-pack battery-powered G2 transmitters receivers, here? The line also includes AC-powered receivers for DJ racks, fixed installations and so forth, as well as mics with built-in transmitters and the SKP100 "butt plug" transmitter.

Sounds mundane, but have you checked the batteries in both the transmitter and receiver? How about the condition and orientation of their antennas?

Double wireless hops are something I'd try to avoid on general principle, but yeah, I can see where it might be necessary or very convenient in certain circumstances. Still, if you can run a cable, that's going to be a lot more reliable and probably better quality too.

- Greg
 
Richard, yes that's correct, getting the audio from the handheld receiver and sending it through another wireless system (G2 body pack) to the camera. The reason - the camera is about 6 meters away from the receiver.
 
It is almost predictable that taking the output of a receiver and feeding it into another transmitter could cause that sort of problem. At least separate the receiver and transmitter as far as possible. Unless the camera is moving around, I would avoid the problem all together by using a hard wire.
 
Greg, thanks for the reply. The handheld receiver is a dual channel unit with independent receivers and antennas for the two mics. It has a mixed audio output to which both the amplifier and G2 transmitter are connected (the signal is split with this audio adapter http://www.bhphotovideo.com/c/product/405051-REG/Pro_Co_Sound_CC_344PC_344PC_Stereo_1_4_Phone.html ). The G2 system is this one http://www.bhphotovideo.com/c/product/324242-REG/Sennheiser_EW112PG2_A_Evolution_G2_100_Series.html . The G2 transmitter is connected to the handheld receiver with a one foot long cable. I don't get interference when I disconnect the G2 transmitter from receiver and use it with its lav mic (to get the sound from the speakers for example, that are a few meters away from the handheld receiver) so I'm presuming the problem is at the connection with the receiver. The levels are fine (-20db on the transmitter, no overload), there's no switch between mic and line type of signal, but as the input reads mic/line, I assume it accepts both. My transmitter is battery powered, but there's some other equipment connected to the same socket as the handheld receiver - the amp, laptops.
Running the cables seems like a good idea also because the handheld receiver has two xlr outputs but I'm not sure I'll get no interference if the problem is the ungrounded electric socket, which I presume it might be although I never experienced anything like that and don't know much about interference from the ungrounded power supply. If that's a known problem, I guess that's what my question would be.

Thanks again,

Dimitri.
Moscow, Russia
 
I don't get interference when I disconnect the G2 transmitter from receiver and use it with its lav mic
Click to expand...

Ah, that may be the key. It sounds like there's some kind of co-interference going on between the two devices. They're operating on widely spaced frequency bands, but when used in such close proximity, you can still get enough RF harmonics bleeding through to cause nasty interference effects.

I can't guarantee this will work, but a ferrite choke on the audio cable between the receiver and transmitter might keep extraneous RF energy out of the transmitter, if that is what's causing the problem. These are commonly used for solving interference problems in the amateur radio community, although I have no idea where you'd find one in Russia. Here's what I'm talking about: http://www.radioshack.com/product/index.jsp?productId=2103222&CAWELAID=107599340 "Bare" toroidal ferrite cores, without the fancy clip/wrapper that's on the Radio Shack device, are widely available (at least on this side of the pond) from electronics parts distributors that cater to the amateur radio hobby or home/car entertainment installation business.

Either with or without this kind of transformer, you might find it helps to loop that audio cable in a tight coil, say 15cm diameter or so. (That would require a longer cable than what you're using, naturally.) Finally, a 1:1 line level audio transformer between the receiver and transmitter would help to electrically isolate the two devices.

All these steps can be used in combination until you find one that works.

I don't know if any of this will actually help, but those are the steps I'd try next.

- Greg
 
Maybe I've missed it, but when you say you are getting interfrence on your signal, just exactly what sort of interference are you talking about? What does it sound like? Hums, squeals, hashy sound, crackles, what?

Would it be possible to obtain a second receiver like the first one in your chain that the mics are feeding the PA with to plug into the camera so you could take the handhelds directly to the camera without needing a connection between the existing PA receiver and the camera at all? Drop the G2 kit out of the picture altogether and use a duplicate of the PA receiver to feed the camera directly.
 
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The Plumber said:
The G2 transmitter is connected to the handheld receiver with a one foot long cable. I don't get interference when I disconnect the G2 transmitter from receiver and use it with its lav mic (to get the sound from the speakers for example, that are a few meters away from the handheld receiver) so I'm presuming the problem is at the connection with the receiver.
Click to expand...

If the UHF transmitting antenna is 'close' to the '900 Mhz receiver', see if you can move the transmitter further away, at least 3 feet or more. Place something like the ferrite choke on the connecting cable.

900 Mhz is an ISM band, and as such anyone can 'play'... ranging from wireless telephones, to cooking/sterilization machines... Well, in the US... in other countries the 900 Mhz band also includes cell phone signals... but probably such equipment for 'personal use' is not allowed...
 
Check the squelch in your receiver... maybe is at high and a little drop in RF make that the signal cut... set the squelch to low is better.
 
OK - let's go through this bit by bit...... The only dual receivers that Sennheiser made that were compatible with G2/G3 were the (now discontinued) EM 550 G2 and the new EM 2000 - both at the top end of the price range. You cannot mix transmitters and receivers between manufacturers (and you can't use 1000, 3000 or 5000 series with ew, only ew and 2000 series.

If you are using 100 series you will need two receivers on two different IM-free frequencies - IE: they have to be in the same memory bank. If you are sending the output of the receivers through another radio link, the frequencies of the second system must be at least 8MHz away from the first system - preferably more.

The close proximity of the second transmitter to the receiver of the first is likely to cause interference. Ideally use a different ew version - EG: A for the first leg and B for the second leg - or use the lowest frequencies for the first leg and the very highest for the second leg.

I hope this sorts it out for you.
 
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John Willett said:
OK - let's go through this bit by bit...... The only dual receivers that Sennheiser made that were compatible with G2/G3 were the (now discontinued) EM 550 G2 and the new EM 2000 - both at the top end of the price range. You cannot mix transmitters and receivers between manufacturers (and you can't use 1000, 3000 or 5000 series with ew, only ew and 2000 series.
Click to expand...

I understood the OP's setup to be 2 unnamed 900 MHz wireless mics and a 900 MHz receiver that had the two channel capability, (or whatever to receive two mics worth of audio...). Then via an audio connecting cable, connected to a Sennheiser transmitter (body pack), which was then received (single frequency in the appropriate Sennheiser UHF band.).

As such, the location of the UHF transmitter relative to the 900 MHz receiver should be 'apart' from each other... despite the units operating in separate 'bands'...
 
The Plumber said:
Richard, yes that's correct, getting the audio from the handheld receiver and sending it through another wireless system (G2 body pack) to the camera. The reason - the camera is about 6 meters away from the receiver.
Click to expand...
Nothing that a 20ft. xlr cable won't fix. HARDWIRE IT!
 
Thanks so much for all the replies. From what I gathered, there's no easy, cheap and fast solution to get the audio wirelessly into the camera. The handheld receiver has to be away from the G2 transmitter for minimizing the risk of interference. Seems to be a high risk of interference anyway. So I think I'm going to try to hardwire and connect the camera to the handheld mics receiver thru two long XLR cables. To the detriment of mobility. Hopefully that will work.
Thanks very much once again, I really appreciate the help and I'll let you know if it worked.
Best regards to everyone,

Dimitri
 
j1clark@ucsd.edu said:
I understood the OP's setup to be 2 unnamed 900 MHz wireless mics and a 900 MHz receiver that had the two channel capability, (or whatever to receive two mics worth of audio...). Then via an audio connecting cable, connected to a Sennheiser transmitter (body pack), which was then received (single frequency in the appropriate Sennheiser UHF band.).

As such, the location of the UHF transmitter relative to the 900 MHz receiver should be 'apart' from each other... despite the units operating in separate 'bands'...
Click to expand...


The OP specifically mentions the ew 100 G2 - hence my reply.
 
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