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Wireless microphones
Wireless mics usually share the airwaves with television stations in the UHF band.

Wireless Microphones: How Best To Work With Systems

To have reliable operation for wireless mics, the first consideration is that the receive antennas must have line of sight to the transmitters.

Wireless microphones give us a lot of flexibility and clean stages.

It’s usually better to operate at the lowest transmit power possible.

That’s not to say that wireless mics, though, aren’t without their limitations.

Over the years, quality and reliability have gone up considerably in terms of wireless mics, among the major manufacturers. Despite this, recent changes to the airwaves have often made them more difficult to use successfully.

In this piece, we’re going to dive in to how these devices work; what’s changed recently that makes them now harder to use; and what you need to know going forward to wisely work with them.

For wireless mics, the RF (radio frequency) spectrum that they work with, it is broken up into several regions. You’re probably familiar with AM and FM radio, for example, which are two bands within the overall spectrum. You may also know of VHF and UHF band television, the aircraft communications and navigation band, and various parts of the airwaves used by the police, for cellphones, and Wi-Fi.

The idea is that everyone using the spectrum is to have their own reserved space, to help assure that their communications will be reliable and available.

Wireless microphones, however, do not have a dedicated part of the spectrum. Instead, wireless mics usually share the airwaves with television stations in the UHF band.

Many years ago, such sharing of space was easy with TV stations, since there was a lot of available unused spectrum. There simply weren’t enough TV stations to fill all the available bandwidth.

Over time, though, the FCC has been selling off large chunks of the UHF band that had once been available, to wireless phone carriers over the last few decades, in a process known as the “spectrum auctions” (or “incentive auctions”). The result? The remaining UHF TV band has been reduced to a fraction of what it once was, leaving many of those using wireless microphones suddenly cramped for space.

Back when the spectrum was wide open, it usually wasn’t too difficult to get a wireless microphone to work reliably. As a result, the market offered an array of inexpensive devices, because their limitations weren’t getting in the way.

Today, with the airwaves being much more crowded (particularly in large cities), those technological limitations are making some wireless mic systems entirely unusable. These less expensive devices simply don’t deal well with crowded and “noisy” environments like we have today, and that very ability to survive in difficult environments makes the higher-end devices more expensive.

One of the most important parts of a successful wireless system is its antenna infrastructure. To have reliable operation, the first consideration is that the receive antennas must have line of sight to the transmitters. In other words, your antennas receiving the signal should be somewhere where they can ‘see’ the microphones, rather than being buried inside a rack or behind people.

The next consideration comes into play when you have more than one receiver: ideally, wireless receivers should share a common pair of antennas.

Most wireless systems come with antennas that can be mounted on the back of the receiver, and I see many people with a sea of antennas crammed inside a rack. The problem is that these antennas, despite being that they are simply there to ‘receive’, will still interact with each other and cause reception problems.

Using a shared set of external antennas (via an antenna distributor) and giving these antennas a good line of sight to the transmitters will make for a much more robust connection. The task of choosing a particular type of antenna is outside the scope of this article but consult a trusted professional for advice in coming to that decision.

You may be wondering why receivers usually include two antennas, as alluded to above. This helps improve the radio link through something called ‘diversity reception.’

As wireless signals bounce around inside of a building, reflections of those radio signals will reach the receivers a bit later than the direct signal from the microphone. Sometimes, when the timing is just right, those reflections interfere with the direct signal and can cause dropouts.

If you use an additional antenna that is slightly separated from the first, though, the two antennas end up receiving those reflections at different times. Normally, when one antenna is getting a degraded signal because of the reflections, the other antenna will be fine. The receiver can then choose which antenna has the best signal at any moment in time.

Even if we’re working with quality wireless gear, and have proper antenna infrastructure, we still have one very important piece to sort out: frequency coordination.

Simply put, this is the science of making sure everyone ‘gets along’ on the air. It’s not enough to just choose different operating frequencies for each device, because there are a lot of phantom RF products created when two or more transmitters are operating at once. This is called intermodulation distortion (often shortened to ‘IMD’ or ‘intermod’). These extra RF products can land right on top of frequencies you’re trying to actually use, rendering them unstable at best. Luckily, it’s not too difficult to go about this process correctly.

First, understand that it’s usually better to operate at the lowest transmit power possible. Many devices have two or more power levels, and users often think that ‘more is better’, but that’s simply not the case.

Think about how difficult it is to have a conversation, while several other groups of people are talking near you. When everyone speaks more quietly, the conversations are easier, than when people shout. With wireless devices, the same principle is true; the reason is that intermod gets worse as transmit power goes up. So, by keeping power low, it’s actually possible to use more channels at once, because the airwaves aren’t getting as crowded with all of the unwanted intermod products.

Second, know that frequencies must be calculated in advance to ensure that intermod won’t be a problem. As I mentioned earlier, you can’t simply choose different frequencies for every device. They all have to be mathematically related, in a way that mitigates intermod problems. The best way to do this is with manufacturers’ free software, which most manufacturers offer, where you simply tell the program your location (so it can look up nearby transmitters in the FCC databases) and what devices you have, and it will help you pick good frequencies.

The alternative way is to make use of the preset groups and channels in most wireless systems. If you stick to a single group, and simply pick different channels within that group for each device, you’ll be OK. Each group has a set a frequencies that are precalculated to minimize intermod with each other. However, never mix and match channels from different groups.

Even with these helpful options to help pick good frequencies, you may still find that the system doesn’t work as expected. That’s when it becomes handy to have a handheld spectrum analyzer. There is an inexpensive product line called RF Explorer, and I recommend everyone own one. This device will help you see what’s going on in the radio spectrum around you and can greatly help troubleshoot wireless issues and find rogue transmitters.

I’d like to recommend some final considerations to help you get the most out of your wireless systems.

The major manufacturers have some great educational resources on their websites, and many also have webinars or online videos that go through a lot of the above content in much greater detail. Study this content – it’s worth it.

You will probably also want to get accustomed to the idea that solid, reliable wireless costs a fair amount of money, but it’s usually justifiable and worth it. Many of the newer digital systems by the major manufacturers, for example, are excellent.

Finally, you may want to consider that not everything needs to be wireless, and sometimes a wired mic simply sounds better and is more reliable (and it’s certainly less expensive).

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