14 Oct The Essentials of Antenna Distribution
When it comes to the world of wireless audio we’ve managed to foster a great working relationship with an incredible company that continues to make steady waves in the industry with patented wireless technology and the ‘wireless wisdom’ to back it up. The fine people over at RF Venue are just a phone call away. Sure, you could call tech support at just about any company but when we’ve got the designers of said technology on speed-dial it’s easy to get complicated questions answered. For years we’ve developed an immense amount of trust with the team at RF Venue so we asked if they’d shed some light on one of the most frequently asked questions we tend to get as it pertains to wireless technology in a House of Worship. Alex over at RF Venue graciously obliged, now it’s time to absorb some wireless knowledge.
Antenna distribution has never been more important than it is today, yet we still see countless audio professionals and technical directors set up wireless like it’s 1999.
Unlike 1999, a multi-channel wireless audio system in 2016 without antenna distribution is not something to party about, or with.
Increased use of multi-channel wireless systems, wireless in-ear monitors replacing monitor wedges, and decreased availability of RF spectrum have strengthened the case for why every wireless microphone, intercom, and IEM should be accompanied by additional tools to ensure flawless performance. Many of these tools fall under the banner of antenna distribution.
**WHAT IS ANTENNA DISTRIBUTION?**
On a basic level, antenna distribution decouples antennas from rack-mounted wireless receivers or (in the case of IEMs) transmitters, and places them in locations that ensure the right signal is transmitted or received from or by the correct wireless device, and that the signal is as robust as possible.
Usually, when antenna distribution is used for wireless mics, the springy whip/dipole antennas packaged with receivers are replaced with higher quality, better performing antennas, manufactured either by the same brand, or by manufacturers who specialize in designing high performance external antennas like Professional Wireless Systems and RF Venue.
(Disclosure: I work for RF Venue. Yes, that is a plug. But I’m telling you about it, so that makes it OK. I think.)
**UNDER WHAT CONDITIONS SHOULD ANTENNA DISTRIBUTION BE USED?**
Antenna distribution almost always improves the performance of a wireless audio system over an identical system that includes no distribution.
Distribution for single channel systems is rare, and usually unnecessary.
However, if dropouts and interference occur, upgrading stock whips/dipoles on a wireless microphone receiver to two external antennas usually provides significant improvement.
For multi-channel wireless systems, for the best sound possible, distribution should *always* be used, especially if those systems include in-ear monitors.
Here are but a few of the persuasive reasons for distributing:
- Antennas + Signal-to-Noise-Ratio:
Antenna distribution lets you do two very powerful things. It lets you choose which specific type of antenna (there are countless designs) is the best type for the venue, and it minimizes the distance between antenna and performer handheld or beltpacks. Both of these maximize signal-to-noise ratio. As I am fond of saying, there are few interference-related problems that can’t be solved by shortening the distance between antenna and talent Tx/Rx, because of the improved SNR.
- Shut down the antenna farm:
Having a large number of stock/whips dipoles behind the rack is bad practice. It’s known as “antenna farming.” Here’s a small, fuzzy picture of unknown origin of a modest antenna farm. Antenna farming is bad for two reasons. First, where antennas do protrude from the rear, they are shielded from the performer by the rack furniture and electronics inside. Even with front-panel antennas, those antennas are at knee height—not good, line-of-sight is always important. Second, packing a large number of omnidirectional antennas into a small space has many potential electrical and RF consequences, especially if transmit antennas are involved. IMD, near-field interactions, proximity to wall-warts and other sources of interference are all reasons to shut down the farm and get wireless consolidated into 2-3 antennas.
- Cable control + management:
When done right, antenna distribution completely eliminates the rat’s nest of power cables, wall-warts, coax, and power strips associated with using multiple channels of wireless audio. Signals are sent through as few antennas as possible, located somewhere other than the rack, all whips are removed, and all mic receivers or IEM transmitter rack units are usually connected to one or more distribution boxes that supply both RF and DC power connections.
- Multi-zone distribution:
Multi-zone gigs or installations are where two or more antennas in separate locations pick up two or more separate signals, allowing FOH to control which mics from what areas (zones) are fed into or kept out of a mix. Multi-zones can be complicated, but they aren’t confusing if designed well. Muti-zone is useful for venues with multiple breakout or meeting rooms, multiple performance areas, or in locations where performers move from the stage (say, “zone 1”) into the seating area (“zone 2”) to interact with the audience.
**COMPONENTS OF AN ANTENNA DISTRIBUTION SYSTEM**
Components include (beside antennas):
- Distribution amplifiers: (AKA, “distro,” “active splitter,” “antenna distributor.”) Distribution amplifiers, or distros for short, are used with wireless microphones. Each distro remotes 4-8 channels of diversity wireless to only a single pair of antennas, via coaxial cable. One, (or a pair), of antennas can be used to receive multiple signals. Those signals are split, re-amplified, and distributed to corresponding receivers. Multiple distros can be daisy chained down the rack to easily accommodate 8-32 channel systems—still through just a single pair of antennas.
- Transmitter combiners: (AKA “IEM combiner,” or just “combiner”) Transmitter combiners do something similar for IEMs what distros do for microphones, but in reverse; combiners take 4-8 IEM transmitter outputs and combine them into a single antenna, which can then be placed closer to the stage for fewer dropouts and happier talent and monitor mixers. Helical antennas are the most popular antenna choice for IEM distribution.
- In-line amplifiers: Are sometimes required to compensate for loss of signal strength (attenuation) along a long run of coaxial cable. As a general rule, in-line amplifiers are not necessary for runs less than 50’ (assuming good quality coax), and only become necessary on runs of 100’ or more.
- Attenuators: Reduce the strength of an RF signal, and are sometimes placed between the front end BNC input on a receiver and the coaxial cable leading to an antenna, to manipulate the noise-floor or prevent overload. Often, less is more.
- Filters: RF filtration is commonplace in broadcast and major events. Filters or devices that include manipulable filters are extremely useful for controlling interference from nearby, unwanted signals.
- Coaxial cable: Coaxial cable is overwhelmingly used as the transport cable for RF signal. In a wireless microphone setup, a pair of coaxial cables connects two antennas to BNC diversity input “A” and “B” on the receiver or distro. Wireless audio is standardized on coax with an impedance of 50 ohms, and higher grades like low loss RG8X are preferred over RG6 or cheap RG8.
- RFoF systems: RFoF is relatively new to wireless audio. The acronym stands for “RF over fiber-optic.” With an RFoF system, a remote antenna is connected to the rack using affordable, durable, lightweight fiber-optic cable instead of copper coaxial cable. With fiber-optic technology, much longer runs are possible, among other benefits.
**STUFF TO KEEP IN MIND**
* Any passive antenna may be used for either transmit or receive applications. When used as a receive (Rx) antenna, the polar plot provided by the manufacturer can be compared to the pickup pattern of a microphone’s response graph. When used as a transmit (Tx) antenna, the polar plot can be interpreted (roughly) as which directions around an antenna will transmit a signal with what relative power. Active antennas do not have this flexibility.
* RF transmitted through coax loses strength in proportion to the length of cable between remote antenna and rack. The longer a run, the more loss incurred. Runs beyond 100’ require RF amplification. In-line amplifiers compensate for loss, but also increase the noise-floor. Low-noise fiber-optic RFoF systems have replaced coaxial cable for many applications with long runs.
* An antenna distro for wireless mics cannot be flipped around and used as a combiner for IEMs, and vice versa.