Planning Frequencies To Avoid Radio Mic Interference

by Andrew Hughes – 27th August, 2015

Radio mic receiver rack

In this beginner’s guide to radio mic frequency planning, we look at how free software can prevent radio mic interference ruining your production.

We’re spending the afternoon testing frequency plots for a customer who is using 30 of our mics for an event at a cricket club.

This is a large number, so requires some careful planning. Before each system leaves us, we check it thoroughly. We set up and co-ordinate the frequencies for best performance. We recommend that you do not alter these unless you are familiar with frequency planning, and are using proper frequency planning software. More on this later!

Frequency Spacing

It’s a common misconception that wireless system frequencies can be spaced evenly across the available spectrum. Radio microphone frequencies interact with each other in strange ways. Frequency A and frequency B can interact with each other to produce frequency C, which could cause interference to another system. This is called intermodulation, and there is a huge amount of maths behind it.

Always speak to the hire company first, before altering their radio mic frequencies. Chances are they are already correctly coordinated. It’s also important to let a hire company know if you are planning on using your own mic systems alongside theirs.

We use dedicated Sennheiser software to plan your frequencies in advance to avoid this. You input the frequency band you are using, any pre-assigned frequencies. The software churns its way through the maths to work out how many extra frequencies you can safely add.

How many systems can you operate ?

It all comes down to your attitude to risk. The more frequencies you run simultaneously, the greater the risk of radio mic interference. For example, on channel 38 we can safely run 12 frequencies. However we know of customers who have pushed this to 16. You can always add external paddle antennas to systems to minimise risk.

If you need advice on frequency planning, call us on 020 3355 8188.

Download the Sennheiser SIFM software here:

See our radio mic range: