Sennheiser Wireless EW100 G2 - Interference

[Dave Mercer]

A few years ago I had a problem with interference in my Sennheiser EW100 G2 mics. The issue seemed to be with the rechargeable batteries I was using.

However the problem is back, despite using brand new duracells.

I've scanned for empty channels, set squelch to LOW, checked cable routing, and done a bunch of other tests.

I also replaced the antenna in the transmitter.

Basically I can get interference even if I'm only 10 feet away from the person wearing the mic, even in direct line of sight. If the person is behind a wall, etc, it's far worse.

I was wondering if the solder job on the new antenna could be to blame. I'm hoping I don't need to buy a new set of mics ....

Thanks all!

[Colin McDonald]

Any chance you could post a sample of the kind of noises that are occurring?

[Battle Vaughan]

I have gotten intermittent interference from cell phones near the transmitter on these units. Blackberrys seem to be the worst. Just a thought... also, it's possible for multiple transmitters to create interference, consult the manual for frequency selection tips if you are using or in the presence of other similar transmitters. It's also possible that there is a strong competing broadcast or other transmitter near your frequency. Sennheiser has a web site that lets you check the open frequencies in the place you are working. I assume but do not know that it is available for your country, worth a look:

http://www.sennheiserusa.com/FindFrequency/

[Richard Crowley]

There are so many possibilities, we can only offer vague guesses by shooting in the dark.
Without more details AND listening to an example of the interference, the best we can offer is sympathy.

[Brian P. Reynolds]

Here in Australia the Sennheiser G2's are in a frequency block that has / or will be taken over by Telcos

[Gary Nattrass]

Never a good idea to use rechargeable batteries with radio mics and they only give 1.2 volts and can cause problems.

The G2 is quite old now and here in the UK only ch70 is not legal for use, it may be that in your country the RF spectrum has changed so I would check that.

Over time radio mics can go off frequency too so it may be they need a service or indeed you need to buy the latest model that will have the correct frequencies as we have had to here in the UK to allow us to use ch38.

It may also be that the replacement antenna is not working correctly.

[Dave Mercer]

Thanks for the reply everyone.

Here's a bit more info:

Mics are: Sennheiser G2 B-Block 626-662 MHz

I experience the problems both in rural and urban areas. Cell phone interference doesn't seem to be the issue.

I live in Guatemala but have had the problems pop up while filming in other countries in Latin America (Costa Rica, Nicaragua, etc). The Sennheiser Frequency Finder doesn't offer up info for Central America.

I've attached a compressed .mov file so you can hear what's going on (I tried to upload a .wav file but DVINFO wouldn't let me).

You can hear three "hits" in the first 10 seconds. I was 2 meters away from the talent, direct line of sight. The "hits" seemed to happen when she turned away from me. Transmitter placed on her hip. Cable was out of the way. Transmitter antenna vertical, receiver antenna horizontal (mounted on hot shoe).

I then moved to about 8-10 meters away, still line of sight. You can hear a lot more "hits."

Fresh set of duracells.

[Martijn Damen]

As far as I know your frequency range is not within the range of mobile phones, 3g and 4g are in higher ranges.
It doesn't sound like a cable problem.
Only thing I can think of is that the receiver antennas are bad .. or you have a monday morning make.

[Richard Crowley]

Your audio sample strongly suggests that you have an intermittent audio/power connection between the body pack transmitter and the microphone head.

I did NOT hear anything that sounded to me like RF problems. (i.e. I didn't hear any multipath hash, or RFI hits, or squelch tails, etc.)

No wireless kits are in the SAME bands as cell phones. (By design.) However cell phones are powerful enough and "wide-band" enough to cause problems to receivers even many MHz away from the operating channel. Furthermore that very sensitive, unbalanced connection between the body pack/transmitter and the microphone head is particularly vulnerable to cell phone transmissions. ESPECIALLY if the subject who is wearing the clip-on lav also has an active cell phone in their pocket (i.e. inches away!)

If a subject is SO IMPORTANT that they must keep their cell phone active while on camera, give the phone to an assistant to monitor from down the hall.

[Greg Miller]

In theory, at least, the polarization of the transmit antenna and the receive antenna should be the same. Either both vertical, or both horizontal. Again, in theory, having them cross-polarized (as you do, with one vertical and one horizontal) can cause a signal strength reduction of 20 dB or so.

Someone will suggest that if you're in a room with a lot of electrically reflective surfaces, the reflections can change polarization to some extent. Be that as it may, the direct signal should be stronger than the reflections. So when using wireless (which I do very rarely) I have always tried to keep both antennas in the same relative polarization.

Incidentally, the same rule applies outside the world of wireless mics. For example, a lot of emergency comm systems use vehicle-mounted antennas, which are vertical. The base station (or repeater) antennas, likewise, are vertically polarized to maximize efficiency and minimize dropouts.

I'm not saying that this will solve your particular problem (I seem to hear a few different things happening), but I still feel it's an important rule of thumb. I feel very safe in saying that if you do this, it certainly won't make your problem any worse, and might improve things significantly.

[Kyle Root]

This is an interesting thread. For a number of years I have had issues with my G-Band G3 wireless set.

When I discovered the Sennheiser Freq Finder site, it made things much easier. I've found that just because the on location scan says that freqs are clear, they may really not be. Using the online site I can clearly find transmitters in a 60 mile radius and see which bands are 100% free of a signal. That's helped a lot.

It turns out, I bought my G-band before realizing that it is a highly polluted range in my location. As such, I've picked up an A-band and a B-band. So theoretically, I figure between those 3 and my backup pocket recorder, ONE of them should be clear! LOL (double mic the minister and double mic the groom at weddings)

[Rick Reineke]

The receiver's built-in scanner is totally inadequate for populated RF environments IMO. I use the on-line frequency finder and/or use an external RF scanner when arriving at the location, then manually check the receiver for extraneous RF.
Additionally the transmitter/receiver 'should be' line-of-sight with antennas and out in the open. The transmitter's antenna should not be touching any skin either.

[Paul R Johnson]

Totally agree on the scan function - pointless, and designed to cause more problems than it cures!

Are you absolutely certain the squelch isn't turned up really high on the receiver? Even close in body masking can reduce the signal briefly below the threshold and you get that quick phut - Richard's comment about a dodgy cable also produces a very similar sound when the power cycles off and on - so well worth checking.

The talent could have jammed the pack in bending the aerial against the metal body - or could have been very close to sweaty skin, again making any of the other problems worse.

It's not interference in the usual sense of interference from other transmitters - that sounds very different, its a lack of signal - either a quick RF dropout or the mic element losing it's power supply.

Both should be easy to replicate - and if, as usual, you find they work perfectly with cable wiggling and waving around, then consider the talent's mic positioning to be possibly the problem.

This kind of problem isn't rare - happens all the time, that's why radios are a pain in the bum,

[Dave Mercer]

Thanks guys.

I've tried two different mics on the transmitter. Both produce the same noise. I think that eliminates the mic cable.

Squelch is definitely set to LOW. I set it to HIGH just for fun and the mic went MUTE.

I placed both antenna pointed down. Cable was clear of antenna on transmitter. No cell phone on talent. Interference seems to be intermittent, until I get about 30'+ from talent, when it becomes nearly constant.

Do I get a local radio technician (generally old guys who've repaired TVs and radios for years) to open it up? Maybe try re-soldering the antenna? Or am I opening myself up to a world or problems?

As an aside, I'm thinking about ordering a set of G3s in any case. Good to have a second set, especially as I live in rural Guatemala. What band should I be looking for? I work across Latin America - have read that G Band (high 500s/low 600s) is reasonably reliable.

[Richard Crowley]

I still don't think it is any kind of RF problem (including antenna).
My money is still on the audio/power connection.
If two different mics show the same symptoms, then my top suspect is the mic connector on the transmitter.

I just DO NOT HEAR ANY kind of RF symptoms in the sample. AT ALL.