Sennheiser G3 Wireless Mic Interference..possibly?

[DH8888885]

I'm having an issue of possible interference on a Sennheiser wireless mic, however I'm skeptical about whether it is just simply 'normal/expected' interference that can be avoided with a channel scan. Grateful for any more knowledgeable people to shed any light on this that they can.

Here's where I am:

1) I have two identical Sennheiser G3 mic/receiver sets that sit in a rack together and plug in to a Behringer X Air mixer. They both run in the same frequency band - the one in the 800s (E?) - and are set up the same (same squelch/db adjustments etc).

2) One started having intermittent static/white-noise on the channel a couple of months ago, which has occurred at 4 separate gig venues now in different parts of the county, from busy town centre pubs to a wedding marquee in a farmer’s field. The other mic/receiver has not had any problems at all during any of this time in any of these venues. The problematic one had previously been fine. The noise happens intermittently throughout the gig and is just short bursts of 'psht'.

3) At each venue I have used the scan function on both sets to find the best frequency and used the first one it suggests (so would assume it’s not likely to be ‘normal’ interference?). I've done the scan just before playing when the venue is already getting full. I've also obviously made sure the frequencies for each set are not near to each other so no cross-communication.

4) In between the gigs I have tested the system at home extensively and been unable to replicate the problem at all - no interference whatsoever.

5) I’ve swapped the XLR cable in between gigs and still had the issue arise on site (so doesn’t appear to be the XLR)

6) I swapped the channel on the mixer and still had the issue (so doesn’t appear to be the mixer).

7) The problem happened recently at a gig when the mic was not there at all (so doesn’t appear to be the mic).

8) The one thing I haven’t tried yet is waiting for the problem to occur then tuning the other receiver, which has not had any problems, to the same frequency to see if the issue occurs on that one too – this would, I think, confirm whether it is an interference problem or something specific to that receiver.

So, with all this in mind, I’m leaning towards thinking that the aerials that attach to the receiver or the cable that connect them are at fault. Perhaps somehow oversensitive/undershielded and getting interference from phones/wifi/etc as the problem doesn’t happen at home but does in busier places?

But I don’t know anything about the inner workings of the box itself, so I suppose it could be any number of things in there too?!

I think I have two final things to test before sending it off to Sennheiser for them to look at:
1) If I tune the working set to the same frequency as the dodgy one, does the same noise occur? This will pin down if it's interference or set.
2) If I swap the aerials over does it still occur? This will give an indication of whether the aerials/cables that connect them are at fault.

Any feedback or ideas welcomed!

Thanks

[AlecSp]

One of the most obvious things to do if you appear to be getting interference/noise on one of an identical pair of radio mics is to swap their frequencies and see what happens. That would help indicate whether it's the kit, or RF interference

Also, try swapping just the transmitter frequencies, then the receiver frequencies and see where the problem follows. That way you indicate whether the fault is with the TX or the RX.

For the bants, it's probably worth trying swapping PSUs as well.

You say you're tuning the two systems far apart to avoid interference, but it's still possible you'd get intermod interference.

When you experience interference, what happens if you turn off the clean system?

Any other RF kit at use in the venues?

Simple problem solving techniques.

And then be prepared for the possibility that you have faulty kit.

[Dave Rowles]

Good advice above. Wireless is tricky to get right.

If you've got the ones with an ethernet port on to connect a laptop, then you can use wireless system manager to check your frequencies are properly free from intermodulation. Plus even though you scan the frequencies during setup, the bands you are using I presume are in the licence free band, so you always run the risk of someone starting up something near you during the gig which causes interference that wasn't there to start with. You can always contact ofcom and try and licence a frequency for the shows, then you...should....run less risk of interference.

[Sam Spoons]

The intermittent white noise sounds like a squelch issue, could it be that the two receivers have their squelch controls set differently, not so much the numbers displayed but the calibration of them? So, does increasing the squelch control stop the issue?

[AlecSp]

The intermittent white noise sounds like a squelch issue, could it be that the two receivers have their squelch controls set differently, not so much the numbers displayed but the calibration of them? So, does increasing the squelch control stop the issue?

Excellent shout. And may be more helpful, as a diagnostic, to decrease the squelch to see if it exacerbates the issue.

And it's a good example of where the basic problem solving techniques mentioned above would point to a single receiver (if indeed this is your issue), as which point you'd double check the configuration between the two to see if there were any difference.

None of this is difficult, just needs to be methodical. And sometimes the answer is the one you'd least expect.

[DH8888885]

Thanks all - some useful tips and I appreciate your time.

I'll try swapping the frequencies on the RX when it inevitably occurs again. I feel like it's unlikely to be a crowded frequency as it's happened four times consecutively on one receiver and never on the other using different frequencies and in different venues. I know it can't be ruled out but seems too much of a coincidence.

Also unlikely to be TX frequency as it happened when the mic was nowhere near (i.e. different part of the country!) so I don't think the problem is stemming from there.

Haven't tried switching PSU's - I'll give that a go too.

Haven't tried switching off the clean system - will do this.

No idea on other RF in the venues.

I'll have a look into the WSM - not used this before so will do a bit of research on how to work it!

Squelch - currently both RX set to the same, but will also try upping it on the dodgy one to see if that makes a difference!

Thanks again, all.

[Sam Spoons]

Squelch - currently both RX set to the same, but will also try upping it on the dodgy one to see if that makes a difference!

Could it be that the calibration is different on the different receivers? Definitely worth a try adjusting the squeltch on the dodgy one while ignoring the numbers.

[Hugh Robjohns]

Swap aerials, too, as one or more might be damaged.

Also, is the receiver near anything digital? Digital audio gear and associated cabling can easily cause interference problems.

[Dave Rowles]

I'd just like to add that I hate wireless. When I have to use it on a gig it always takes far more time and effort to set up than a long cable. Even those gigs where I have a dedicated wireless tech are always stressful. Spent a whole 8 hours trying to beat a 32 channel Axient system into submission once, and that was a combination of frequencies, dante, workbench, and firmware mismatches to work through.

I'd rather rip a 80m 64 channel multicore out of the ground after a 3 day festival to be honest.

[zenguitar]

I'd rather rip a 80m 64 channel multicore out of the ground after a 3 day festival to be honest.

And have no doubts, that's not something to look forward to with anything other than dread.

Andy

[g18llo]

For the bants, it's probably worth trying swapping PSUs as well.

I'd upgrade that from "bants" to "absolutely"; I've had similar issues with my PSM900/1000 setup, Shure UK traced this back to a power issue and as a result made global changes to the P9T transmitter.

I also had the same issue with my UAD Apollo live, which I used for effects, and that was traced back to the PSU too. In the studio, silent, live stage, constant interference.