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After the initial setup, wireless mics generally drop out because of loss of range and multipath reflections that cause cross-polarization fades.
Loss of range is typically caused by competition from localized interference, such as that caused by TV stations, motors, LED lighting, anything with a computer chip, and now cell phone service in the 600 MHz band. These sources, added together, form your noise floor. Directional antennas and bandpass filters can work together with high-quality coax cables to help mitigate this problem.
Multipath interference is caused by reflections of your transmitter’s signal, primarily by metal objects in your venue and other boundaries. These reflections flip polarity and arrive out of phase which causes cancellations in your receiver’s antennas.
Cross-polarization fades (aka signal cancellation) happen when your direct signal and reflected multipath signals mix in your antennas. This can be somewhat mitigated by proper antenna positioning. However, since multiple antennas must be separated by distance to avoid interfering with each other, the signal in each antenna will not be in the same wave period (phase). Our patented Diversity Fin antenna solves the distance problem by being co-located, while orthogonally mounted elements eliminate cross-polarization fades. Not only is it more convenient, it is actually better than two “paddles”: It doesn’t drop out!
Typically, the specs for unlicensed wireless mics (≥ 50 mW) call for an approximate 300’ range, but this range depends on the signal not being compromised by local interference. The same mic that may perform flawlessly for 1000’ or more in an open field in the middle of nowhere may not work at even 50’ in an urban environment. Your actual range depends on getting a signal that is sufficiently stronger than the local noise floor (interference) at your venue. You can perform a “link budget” calculation to get a more precise answer to the question.
If additional range is required, switching to an antenna with more gain or a coax cable with less loss is needed. Antenna booster amplifiers do not increase range and should not be used in an attempt to boost range. They should only be used as a last resort if suitable signal strength cannot be achieved any other way.
Yes, as a general rule: Wireless mic systems, distro systems, antennas, and coax cables from nearly any brand can be successfully used together, provided that they operate in the same frequency range and within the rated power levels. You can add an RF Venue distro to an existing distro from another manufacturer to provide for additional wireless mic systems. It is unlikely, however, that you could mix a transmitter from one manufacturer with a receiver from another even if the frequencies match because of their coding schemes.
Since July 3, 2020, most users can use the 470-608 MHz and 614-616 MHz bands as well as a portion of the 600 MHz duplex gap (657-663 MHz). Operation above 608 MHz will typically be unrealistic for most users. If your wireless systems have the ability to tune outside these frequencies, even if you don’t actually tune to them, they have been decertified for legal use in the USA. You can check with your wireless mic manufacturer to see if your decertified systems can be updated.
Unlicensed wireless microphone use is also permitted on the 902-928 MHz ISM band, the 1920-1930 MHz band, and portions of the 2.4 GHz and 5 GHz ISM bands under specified power levels and rules for operation for each band. In addition, the VHF frequency range for wireless microphones of 168-216 MHz is available.
Many wireless mics incorporate a “squelch” system to aid in the reduction of unwanted audio noise while using an analog wireless microphone. When a transmitter is turned off, the squelch pilot tone is no longer transmitted to the receiver, so the receiver increases its range looking for a signal. It inevitably finds interference; since the receiver is no longer muted by the squelch tone, that noise is passed on to your audio system.
Your squelch level is usually set at the factory based on the use of the supplied whip antennas for your receiver. When an antenna distribution system is employed, the system gain will usually change a bit, and the squelch will need to be readjusted. This is a simple procedure and will probably result in better performance than factory-set levels.
One of the most important steps for ensuring reliable system performance is to select the best possible combination of channels for your wireless mics and IEMs. As you add more devices, the number of open frequencies begins to diminish quickly. In the past, channel selection was relatively easy, but since we are typically working with only 6% of the bandwidth we had only a few years ago, proper selection has become much more critical.
Many wireless units come with automatic channel finders. They are better than nothing but may not work well depending on local conditions, especially when using mics and IEMs together. The gold standard is to use an RF scanner and insert the data collected from it into an RF coordination program—many manufacturers offer free versions. These programs can often use wireless receivers as input but, remember, receivers can only see the frequency range to which they can actually be tuned. They cannot consider additional channel blocks or out-of-band interference, which can lead to results that are less than optimal.
Proper antenna aiming can result in free benefits, so don’t ignore it. Omni antennas, such as the whips that are provided with a new wireless microphone, pick up in a 360° horizontal circle, so they cannot be aimed. They provide low gain and no rejection of local interference. Directional antennas (paddles and helicals) provide additional range and typically reject 50% or more of local interference.
The horizontal coverage angle of directional antennas is primarily what to consider when aiming antennas. Basically, the task is to visualize a triangle with the pattern of your antenna and lay that over your floorplan in a way that includes all the positions you need to cover for your performers. This can often be improved by connecting your RF scanner to your antenna and making relative measurements at a few positions. In some cases, signal improvements of up to 20 dB can be achieved by simply moving your antenna to a different position only a few feet away from its starting point.
Except for Diversity Fins—which have the added benefit of having co-located antennas, so the signal in both antennas is in the same phase period—antennas need to be a minimum of a quarter wavelength (6") apart from each other, though they are much better at two wavelengths (44”) apart. However, that is still not far enough away from each other to prevent interaction between the antennas. It may not seem intuitive, but some of the power received by your antenna gets reflected (VSWR or return loss) out from the receiver and back into the receiver’s antenna, where it now becomes a transmitter. If one antenna is within about 6" of another antenna, their signals will imprint onto each other causing interference. This is the major reason “antenna farms” should be avoided at all costs.
How will you know if your model wireless system connected to your antenna with your coax cable lengths will reliably perform in your venue? Plugging some specs into the Link Budget Calculator below will give you a pretty reliable answer. Basically, you add all the gains and subtract all the loss figures (in dB) and hopefully end up with a number that is at least 20 dB above the number (in dB) for your local noise floor.
For the best performance and easiest setup, when using multiple channels of IEM they should be connected to a combiner and then retransmitted via a single helical antenna using the lowest gain setting that reliably works on your transmitters. The use of multiple transmitting antennas on multiple transmitters almost always results in signal degradation. We recommend feeding no more than eight transmitters into a single combiner system as exceeding that number rapidly increases the probability of IM (intermodulation) interference and results in the likely reduction of possible open channels for both your mics and ears.
Helical antennas are overwhelmingly the antenna of choice for IEM transmission because the circular motion of the RF field emitted distributes the signal through all possible polarization angles. This removes the greatest risk of dropouts, as most IEM belt packs are limited to a single whip antenna.
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St. Edmunds Church in San Marino, California, and the Colonel Bill Barber Marine Corps Memorial Park in Irvine both had RF coverage problems with wireless microphone systems, and both benefited from RF Venue’s Diversity Fin Antennas, with the RF Venue DISTRO4 RF distribution amplifier servicing St. Edmunds’ multiple receivers. Ashland, MA, USA, February 9, 2022 — When someone ...Read More
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