We’ve already discussed the basic hardware, technology, and frequency planning of RF mics. This segment discusses setting up and troubleshooting your system.
The wireless mic’s receiving antennas need a direct line-of-sight view of the area where the transmitter will be used. This location may be where the receiver itself is placed, or it may just be the site of the remote receiving antenna, with the receiver mounted somewhere else. In the latter, it is absolutely critical that appropriate RF antenna extension cables of the proper type are used as an improper cable type can ruin RF performance. Any reputable wireless mic manufacturer will offer instruction and assistance on this. If the stock receiver-mounted antennas are used it is often best to splay them in a “non-parallel” manner, 90 degrees, and the manufacturer should offer further instruction on antenna orientation.
If the TX has an audio gain adjustment, it should be set up to achieve as high a modulation as possible without ever over-modulating. Remember, avoid overmodulation – if the audio signal becomes overmodulated in the TX it will be reproduced that way in the receiver and can NOT be corrected downstream!
The spectrum/frequency planning that applies to single channel operation still applies for multi-channel setups, but since each radio mic needs its own operating frequency much more open spectrum is required! Further, in addition to needing to be on separate frequencies, these frequencies must also be on cleverly spaced intervals to avoid intermodulation interference among themselves. That’s part of frequency coordination. It is complex, but fortunately the manufacturers have already done this math (or should have!) for multi-channel capable systems. Very simplified: When multiple wireless are running simultaneously they produce RF energy on additional frequencies (intermod products!). When frequency coordination is correct, these intermod products are still present but do not land on (or near) the operating frequency of any wireless in the system. This is why it is not recommended to change the frequency of one wireless mic in your multi-channel setup without considering ALL of the operating frequencies of the systems as a whole – just one change and we might throw off the math and cause new intermodulation interference problems in one or more of the wireless systems. The goal is multiple system frequency compatibility (defined as the condition where two or more wireless microphone systems are operating simultaneously with no degradation in the performance of one due to the presence of the other systems). There is far more to multi-channel frequency coordination than can possibly be covered here. Go with a good manufacturer, rep, or dealer that you trust.
When running several or many wireless microphone systems together it is advisable to use one or several master antennas, instead of relying on the “antenna farm” that is created with stock receiver antennas. If diversity receivers, just 8 receivers will already have 16 antennas! But optionally, one single diversity pair of antennas can be distributed to each receiver with the appropriate hardware (instead of 16 antennas, we then may have only two). Master antennas are fed through antenna distribution networks (passive or active) to achieve this and most major wireless mic manufacturers offer antenna distribution systems for use with their wireless microphone systems. Distribution systems may be employed whether using remote-mounted or local receiving antennas. There are also often various types of optional receiving antennas (active/passive, directional/omni, etc.) for reception.
We can’t cover all the details of multi-channel operation, but here are a few brief, general operational tips:
o Know your gear well.
o Plan frequencies, or frequency ranges, prior to purchase (with support as necessary).
o Keep distance between TX and RX antenna line-of-sight and as short as practical, but do maintain a bare minimum distance of at least ten feet (or the specific manufacturer’s recommendation), preferably more. TXs too close to RX antennas can cause overload.
o Maintain distance between multiple transmitters. Transmitters in close proximity to each other will degrade performance (don’t line up your bodypack TXs next to each across the sound booth ledge when doing headphone checks!). Space them out, even during equipment checks.
And a few troubleshooting tips:
o Consider the presence of other devices in your facility that could possibly cause RF interference (RF assistive listening systems, DSPs or computers near receivers, wi-fi networks, etc.)
o Consider “time of day” patterns if troubleshooting interference
o Turn off the transmitter, keep the receiver on, and monitor the receiver (meters and audio). If there is indication of RF (RF presence meter on RX or audible noise) this is a sign of local RF energy – potential interference. If this energy is low enough in level, “RF capture” can work – that is, always keeping the associated mic transmitter turned on may “capture” the receiver and keep it quiet (not a great long-term solution), masking the potential interference. Do the same test for each system in multi-channel setups.
o Turn all receivers on and all transmitters off. Turn on one transmitter at a time and expect to see good RF performance on its associated RX, but no indication on any other RX. Do this with each TX – only one on at a time – and then gradually turn on two together, and so on… This can uncover great clues as to if (and where) incompatibilities exist.
Wireless microphone technology has progressed rapidly and offers incredible flexibility and creativity in our worship venues, without doubt. But product quality does vary greatly, and poor wireless performance is surely even more distracting than the option – a cable. Not everything has to be wireless on our church platforms. A few good quality channels of wireless may be a far wiser investment than many channels of poor equipment.