Buyers' Guide: Radio Links
When choosing wireless RF links it is important to consider frequencies, versatility and latency. And make sure you test the kit first, says Chris Brandrick.
Pinpoint the application
Think about the environment you are going to be in, how long you will be using RF for and the reliability desired. “If you’re doing a marathon then your RF coverage from motorbikes at the front of the race will be critical for telling the story,” says Chris Brandrick, sales director at Broadcast RF.
“Sometimes you are the only AV source. In that case, invest heavily in RF which includes using planes at high altitude (to negate low-lying bad weather) and multiple reception sites.
“However, there is a growing interest in lower cost, fun, solutions where you might slap on a camera and RF unit to a BMX bike, for example, and see what you get back. The links are not essential to your coverage so you can afford to go with a GoPro and more of a budget links option.”
What’s the frequency (Kenneth)?
Some systems operate licence-free over the standard DVB-T 8Mhz radio channel or the 5.1 – 5.9 GHz band used for public Wi-Fi. These are versatile and typically work out cheaper. However, bandwidth can’t be guaranteed which is why you may prefer product operating in licensed frequencies. Vislink, for example, claims efficiency gains can be made by deploying its own LMST (Link Modulation Scheme for Terrestrial) RF microwave links. Licenced frequency links are typically preferred in environments where you have control of the spectrum, such as in indoor sporting arenas.
We want kit that can be used anywhere: bike, plane, helicopter, back of a camera. It’s got to be as versatile as possible.
Do plenty of testing and research
It’s an obvious point really (but a sound one nonetheless) that you should, where possible, turn the expertise of companies with experience of operating in many scenarios to your advantage. “Every venue is different so take the advice of companies like Broadcast RF and others who hire a range of kit, to understand what the issues are because, believe me, they are multiple and diverse,” says Brandrick. Test the kit before purchase ideally in the venue intended for use; even better side-by-side with a different model.
Make sure the kit is versatile
“We want kit that can be used anywhere: bike, plane, helicopter, back of a camera,” he says. “It’s got to be as versatile as possible. Watch out for kit that can only be used in point-to-point applications.”
Power is important
The lower the power consumtion, the fewer the battery changes. “That’s pretty important on lengthy live coverage,” he says. “Cameras have generally got bulkier in the move from SD to HD, and battery performance generally depends on camera size. Our golf radio cam systems can achieve an hour live roaming the whole course. Or it can last for half of a football match (incidentally it’s always prudent to change batteries at half time).
“At Broadcast RF we have to be the camera-op’s best friend. They don’t want to be lugging around a lump of metal for 90 minutes – so anything smaller with better power consumption that requires less battery changing is all good from their point of view.”
The smaller you go generally the hotter the links unit gets. Smaller units will probably not have side panel controls so you trade size for being able to freely change the camera settings. “Consider whether you want to be able to change frequencies easily in a live scenario by pressing button on the camera – rather than having to plug it into a laptop.”
Latency is vital
The way the signal breaks up – or doesn’t - is clearly vital. You don’t want freeze frames or slow wipes (refreshes) across the screen which makes it very difficult to stay on air. “It’s physically impossible to achieve zero delay but latency with HD is down to around 20 milliseconds (using Vislink L1700). That is genlocked and permits RF at music concerts where lip sync can be an issue.”
Interview by Adrian Pennington
Picture: Vislink kit being used to cover the London Marathon.