Radio mic distortion

[Original Beef]

I was running sound for a school musical this week and encountered a problem. I was using the schools Sennheiser G3's 4 channels of CH70 with rf distributor, my Sennheiser g2's on 830 MHZ -832 MHZ running 4 channels and rf distributor. I've used these with this school many times in the past with no issues. This week however they required an extra two mics so I used two Sennheiser XSW-2 systems on CH 38 using the whip aerials.  All was fine during the two days we rehearsed but during the first show with an audience one of the XSW mic's was extremely distorted and practically unusable. I only had 20 minutes during the break so after locating the transmitter checked the capsule first to see if that was the problem but it was fine. I changed frequencies and it improved a bit but was still quite bad. We had further rehearsals the day after plus a matinee performance so I changed the frequency again and it was fine during the day  but it started to intermittently distort again. Not as bad as the day before but it was certainly a problem.

The only thing that changed as far as I am concerned was the two night time performances were populated by 250 adults mostly I'm sure with mobile phones and the matinee was with primary age school children who I assume didn't have mobiles, so I am wondering if this was causing a problem. It must be noted that despite the distortion I had a full RF signal at all times and there was no ghosting or searching for signal etc. 

 

Does anyone know what happened here please?

[Robin D]

Was there line of sight from the mic to the receiver? Or did the audience act as a barrier? Has similar with some Trantec units and had to move the receiver rack to solve it. Yes phones are an issue. Ask that they turn them off. Not all will but 200+ looking for a signal, and a lot probably looking for WiFi will create a lot of RFI. Not everyone will do as you ask, but many will if you point out that it's not the most modern of equipment you are using and by leaving them on, they may well spoil their child's performance. 

Had another issue when going back to a venue where all had worked seamlessly on a prior occasion to find I had placed the racks within a few feet of a newly installed WiFi access point. 

[Original Beef]

Thanks for your reply.

The audience where to the side and behind the receivers, and at the interval I was 3 feet away when trying to sort out the problem and it was still there. At all times I had full RF with no drifting.  I'm not convinced the phones were the problem but it was the only variable so I may be clutching at straws. It is also entirely possible there is an intermittent fault on the transmitter or receiver.

[sandall]

If you were that close to the stage were you maybe overloading the receivers (XSWs are probably not as robust as G2s & G3s)? 

[Lamplighter]

The Sennheiser quick guide to XSW2 shows a minimum of 5 metres between Transmitter and Receiver. The other consideration is to run an intermodulation check across all channels in use.

[Alec]

What was the physical separation between all the systems - most notably the two additional ones?  I'm guessing they were just piled in.  Spacing them out can do wonders with intermod