Visualising the RF Environment
Project Engineer, Stuart Stephens talks us through the importance of visualising the RF landscape.
Why would we want to do that? I hear you ask....
The reason for RF visualisation is simple: When setting up our wireless rig, we need to maximise the amount of channels we can have on air and ensure reliable performance by understanding what spectrum is available and which other users could cause interference.
Example Sources of RF Interference:
TV Transmission: Since the digital TV switchover, analogue television has ceased to be an issue in the UK. In some European countries, however, analogue TV is still in transmission so do ensure you take this into account while touring. For us here in the UK, digital transmission is the primary concern.
The best way to ensure you avoid interference from TV is to use RF coordination software (such as Shure's Wireless Workbench), which allows you to enter the postcode of your venue to receive TV transmitter info in the surrounding area. In conjunction with this, it's recommended you also check the PMSE database to check field strength data; this will provide you with further insight into which direction the channel is transmitting.
LED Walls: As part of modern production values, these devices are a fact of life at most large events. Unfortunately for us, these devices actually output a large amount of RF signal, which can be problematic if your antennas are not placed very carefully. It might be tempting to place your antenna on top of the LED wall to gain direct line-of-sight, but in reality, your antenna now has to fight through a whole load of extra noise.
Finally, and perhaps most obviously, we also need to consider other wireless microphone users. Everything from in-ear monitors to basic intercom systems could all be sharing the same space. By correctly visualising the RF landscape, we can help mitigate the risk from these users – and the other sources mentioned above – to ensure your show runs as smoothly as possible.
RF Scanners
To accurately assess the RF landscape, we need the support of a good quality scanner. Scanners vary wildly in cost from a few hundred pounds all the way up to a few thousand. While there are many differences between cost-effective models and higher-end options, one of the key differences lies in measuring the noise floor.
Lower priced scanners will give you an indication of what's happening across UHF spectrum, but they fail to dive deep and reveal the true detail. Higher-end scanners are capable of measuring a lower noise floor, and thus, reveal more potential sources of interference.
If you don't have access to a stand-alone scanner, you can, of course, scan using any of the Shure networked receivers. In this instance, though, you are limited to the tuning bandwidth of that particular system. This limitation is fine if you're only deploying mics within that particular systems range, but if you're setting up multiple systems across different bands, it makes sense perform a full wideband scan.
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Signing off
We hope you found our brief overview of RF visualisation helpful. To learn more, consider attending one of our Wireless Mastered or Wireless Workbench training sessions.
