Radio Mic Ranges. Recommended?

[Gongalong]

Hi All,

 

We have two Sennheiser radio mics (EW100 G3) we use in a hall, and every now and then we get a burst of noise/interference. It only lasts for a second, and is fairly infrequent. I've asked Sennheiser, and they don't have any recommendations of frequencies to use.

 

Currently they're tuned to Bank U.1 864.1MHz and Bank 1.1 863.1MHz,

 

Does anyone know if these aren't great frequencies to use in the UK, or conversely have recommended ranges to use?

 

Thanks

[Andycat]

863.1, 863.7, 864.1 and 864.9 MHz are the usual ones if they're the free range. You have a lot more control if you're licensed. Taxis, Security and all sorts of other radios can mess with the free channels.

 

There are postcode specific ranges that I just can't find for the licensed mics. We've had no trouble once we used those!

 

Good info here:

https://www.ofcom.org.uk/manage-your-licence/radiocommunication-licences/pmse/pmse-licence-info

[smurfomatic]

The mics we use for our PA are 863.3 and 864.3 MHz, the same model also operates on .1 and .8 frequencies so maybe these can be tried?

[Oaktech]

Worth checking if your equipment has pilot tone capability and that it is turned on as that can help prevent inter-mod issues.

 

It might be worth tabling an upgrade to some 2.4ghz as they are much more resistant.

[Andrew_C]

Canford Audio have a useful guide. And I remain to be entirely convinced by the 2.4GHz idea - that spectrum is already crowded, and some of the stuff doesn't play nicely with IT WiFi. Stomps all over it, in fact.

 

Infrequent bursts of noise could be coming from equipment switching near you. Things like - microwaves, lifts, fan motors, unsurpressed car/bike engines, etc. Try to tie down a timing / interval.

Edited June 8, 2021 by Andrew_C

[Techie-v2]

Have the same issue with the same mics.

I asked our AV servicing partner about it, his answer was plain and simple, get licenced ones.

 

Trouble is no one wants to spend the money, yet they complain when we have the issues.

[Chris_Cook]

It sounds like wide band interference, so probably not a lot you can do other than getting licenced ones.

 

However there are a few things you can try. When do you get the noise? Is it when someone is talking into the mic, when the transmitters are on, or when the transmitters are off?

 

Firstly on Sennheisers, you should have both mics on the same bank to avoid Intermodulation interference. One of yours is on the user-specified bank (u.1). Try changing that to 1.2, or 1.3 or something starting with a 1.* I'd avoid the U bank unless you absolutely need it as its not guaranteed to be free from interference.

 

If there are any other radio mics in the near area, you might need to co-ordinate with them on channels They all need to be on the same bank, but different channels - which can be tricky if they aren't from the same manufacturer. Shure and Sennheiser publish the frequencies they use for each channel.

 

There should be a 'squelch' setting on the receiver. Turning this up a notch or 2 may well sort this issue out. The receiver should mute its audio output when it doesn't get a signal. This model doesn't check if its a valid signal or interference, so a burst of RF energy can cause the issue you describe. If you turn the squelch up too high, then the audio might cut out. I wouldn't go much above 25-50% unless you get good signal from the transmitters.

 

You might also be able to relocate the receiver if its near any lighting kit, electric motors or other noisy equipment.

 

Edit: I'd also check the batteries if you've not done it already. You can get weird issues when the batteries start getting low. The battery meter probably isn't that accurate, So I'd always put new batteries in when using them for an event. Remember rechargeable batteries have a lower voltage which can affect things.

 

There should be a gain setting on the mic. If you get the burst of noise when someone loud gets too close to the mic, turning this down might help with that. You would need to adjust the gain on your sound desk to compensate. If I remember rightly, the handhelds you have to remove the capsule to get to the switch, and the belt packs is under the flap or in the menu.

 

I think this is an older model, so its also possible that the mics or wires are damaged. This can especially be the case for lapel/headset mics. In this case, you might be able to replace just the mic, rather than the whole thing. You can test that by gently shaking the mic and seeing if you get the noise. The cables between the receiver and the sound desk or the sound desk and the amp could also cause issues if they can be disturbed.

 

You can also hire radio mics if you want to try different bands. We use a company called Radio Facilities in West London. Most AV companies should have a set for hire though, and may be able to give local advice.

Edited June 9, 2021 by Chris_Cook

[howartp]

If you're going licensed, there's two types of licensing - shared and coordinated.

 

Both cost money, but shared is as it says - still shared, so you've not guarantee that the pub next door doesn't have the same shared license.

 

Coordinated assures you that nobody else can legally use your frequencies in your area.

 

At my school we have 23 frequencies in use with Audio Technica; 4 on the free frequencies, 11 on shared and 8 on coordinated.

 

Peter

[Gongalong]

Thanks for all the replies, much appreciated.

 

When do you get the noise? Is it when someone is talking into the mic, when the transmitters are on, or when the transmitters are off?

It's fairly infrequent which is part of what makes it difficult to troubleshoot. Sometimes just once in an hour, or worst case a couple of times in 10-15 minutes. It's only when the transmitters are on. The noise itself is just a second or so of very loud white noise, so it makes everyone jump. I'm sure it's interference of some sort, but I can't think of anything that's nearby that's an obvious cause.

[Andrew_C]

If only when the transmitters are on, I'd be looking for faults in one of them. Try to borrow a new transmitter, and see what happens.

[Oaktech]

[snip] And I remain to be entirely convinced by the 2.4GHz idea - that spectrum is already crowded, and some of the stuff doesn't play nicely with IT WiFi. Stomps all over it, in fact.

 

You're right, however, that wasn't the question... We need Radio Mic, not WiFi at this moment...

[SamanthaD]

First off, good advice about having both mics on the same bank as each other. Looking at the Sennheiser chart here I'd recommend using Bank 1 Channels 1 and 2 (page 17 for your equipment I'm guessing).

 

Second, make sure pilot tones are turned on both on the transmitter and the receiver.

 

Third - licenses do not guarantee no interference. We have site specific (co-ordinated) frequencies running across 3 channels on a frequency range not standard in the UK (Channels 28, 29 and 31) and still get interference from time to time. On Channel 70 you really take the chance I'm afraid.

 

Fourth - if you want to go digital look at kit that's based in 1.9GHz band (DECT), not 2.4GHz. You do pay with a little latency increase, but if it's just spoken word or non-critical applications it can work really well.