Radio mics and amps

[conan]

Hi There

I am doing the sound for and opera and I have a few problems with my radio mics. 4 of them are cutting out and are very noisy. They are Set to frequencies that have been tried and tested. They are hooked up to an antenna distro and have areals with antenna boosters on them, The are about 1ft away from stage. Any thoughts.

 

 

Also could you explain that the bridge function on an am does and what is the impedance and how does it affect the system.

 

 

cheersv

[Ynot]

Hi There

I am doing the sound for and opera and I have a few problems with my radio mics. 4 of them are cutting out and are very noisy. They are Set to frequencies that have been tried and tested. They are hooked up to an antenna distro and have areals with antenna boosters on them, The are about 1ft away from stage.

1. Are those frequencies LICENCED to the venue? If not they MUST be (unless they're de-reg frequencies)

2. If they ARE de-reg freq's, then that may be part of your problem, as some of those do have intermodulation problems.

3. Are you using QUALITY batteries (alkaline, preferably Duracell/Procell)? NOT a good idea for some mics to use re-chargables.

4. If the receivers are connected to an aerial distro AND a signal RF booster, then WHY is that kit only a foot away from the stage? You may find that there's just TOO much RF signal competing there, so why not remove the receiver set up to the booth, where it really should be anyway?

Also could you explain that the bridge function on an amp does and what is the impedance and how does it affect the system.

5. The bridge function usually sums the outputs of a stereo amp and creates a single mono output.

6. Impedance is (in VERY basic terms) the value in ohms of the speakers and the output of the amp. Ideally you need both to be matched to achieve the most efficient power transfer from output to speaker. It's generally NOT A GOOD IDEA to try to run an amp with speakers less than the minimum spec'd impedance for the output characteristics - ie if your amp is quoted as compatible with 4 to 16 ohm speakers, it will also quote the minimum size of speakers that should be used (eg 200W into 16 ohms, 400W into 8 ohms or 800W into 4 ohms - and before I get flamed, I KNOW it's not quite THAT simple!! :D) - but don't try to run an amp spec'd at a fixed 8 ohm using 4 ohm speakers.

[Beanzy]

Amp impedence as outlined above but impedence for the RF system the will be another thing altogether. most radio mics rely on an antenna system with a nominal impedence of 50 Ohms, although the actual figure will depend on how well the system was installed in the first place.

 

You may be suffering from any one of many possible sources of interference. People can only take pot-shots at guessing on-line. You should get someone competent on-site to check the system out.

 

If you're in an amateur situation then you could do worse than dig out someone from a local RSGB club who has the necessary kit to pinpoint the source of your interference. The have a section dedicated to advising and trouble-shooting EMC issues if the source is ham radio. Their site's at rsgb.org.

[paulears]

If they cut out and are very hissy and noisy, then with your aerial system 1 ft from the stage it is rather odd to get weak signal symptoms. The obvious thing is to test them one at a time - are they all noisy - if so, I'd suspect the ADU - try plugging a single aerial into one of the receivers, does the problem go away. If it does, suspect the distribution system. With the transmitters off, do any of the receivers show any signals on the input? If so then interference is a definate possibility - asking the local radio club is one solution I hadn't thought of - although a car park full of brown Skodas and allegros with massive pylons on the back might be worth a picture or two - make sure you have plenty of tea on the go and somewhere they can hang up their anoraks!