Understanding radio mics

As this is the tech talk column I thought it may be a good idea to cover some of the common problem areas and start with this common problem. Now you will see mics with 16, 32, 300, 700 or 1440 channels, this does not mean that you can use anything like that number of mics together. Radio transmitters are like musical instruments [in that they produce harmonics which are multiples of the base frequency], and these harmonics interact with each other to restrict the number of usable channels. As an example, the Redback 16 channel mics have 6 channels which can work together, the main mics I hire are the 700 channel series but only 16-17 channels will work together.To get more channels I am now getting in the Sennheiser 1440 channel units and while they are coy about exactly how many channels I will get, it should be 24+. Now other areas to consider are interference from other radio sources like in ear monitors, which tend to use the same bands and radio talkback systems which I am now also importing as prices are lowering. If you are using half a dozen radio mics there is not likely to be a problem but once you start adding talkback and in ear monitors you will need some specialized assistance. And as I said in an earlier piece, the radio part is only the beginning, the complexity of multi mic mixing a live show added to the potential harmonic interference means that rehearsing with the full system is crucial and failure to do this and find potential problems can lead to disaster. In short, radio mics are not a panacea so please bear this in mind.