TYPES OF WIRELESS MICROPHONES

Wireless microphones can be categorized as handheld, body pack, or plug-on; VHF or UHF; and diversity or non-diversity.

Handhelds refer to the handheld microphones that have transmitters built into them. They are popular for vocalists and variety stage performance. Body packs consist of transmitters only and can be thought of as "wireless cable" rather than "wireless mics," since any microphone (with the appropriate adapter cable) may be plugged into them. Body pack transmitters are generally used with lavalier microphones. Wireless units can also be used with a condenser mic on a fishpole or a stationary mic planted on the set.

Wireless mics can be VHF or UHF. Most professional units share the upper VHF television bands (TV channels 7 through 13). If you expect to be shooting out of town or on the road, make sure there are no local TV stations broadcasting on the same frequency as your radio mics. For instance, manufacturers' designated (A) "traveling" channels (169-172 MHz) are popular for use in most places across the United States.

Wireless microphones are available in the UHF frequency range. The UHF frequencies, compared to VHF, are less susceptible to most common sources of radio interference. A greater number of UHF units can be operational at the same time without cross interference, a definite advantage when doing stage and variety work. Another advantage of UHF is that the transmitter antennas on the body packs are very short and do not require careful rigging to the actor's clothing.

"Diversity" receivers work on the principal of switching between two receivers, with antennas placed at least 1/4 wavelength apart. The diversity unit compares the incoming signals continuously, and instantly switches to the better signal, thus eliminating "drop outs" or dead spots.

Body Pack Application:
Without question, the most difficult aspect in using radio mics is correctly attaching them to the body of the talent.

Body pack transmitters can be hidden almost anywhere. The most common sites include the small of the back, rear hip, inside thigh, ankle, pants pocket, and inside chest pocket of a jacket, or in the heroine's purse. When talent is wearing a scant bathing suit, for example, radio mics can sometimes be hidden under straw hats, or even on the back of the neck under long tresses of hair. Leg warmers provide a convenient place to hide radio mics when dealing with exercise attire.

There are a number of ways transmitters may be secured. Belt clips work fine under a jacket or loose top. Special pouches or pockets can be pinned (or permanently sewn) into wardrobe. Sometimes it is possible to merely hang the unit with a safety pin that has been taped onto the transmitter casing. Specially constructed elastic belts known as belt and pouch kits, such as those manufactured by PSC, can be worn around the waist, thigh, calf, or ankle. Transmitters can be also held in place by elastic bandages.

Any time camera and gaffer tape is used, special care must be taken not to tape directly to skin or delicate wardrobe (such as nylon stockings). Fold the tape over itself to form a non-adhesive strip to wrap around first. Better yet, use some sort of liner, such as a strip of cloth. Avoid placing the transmitter directly against the skin, since body moisture tends to interfere with (absorb) the outgoing signal.

Care should be taken in securing the flexible transmitter antenna cable. To prevent the antenna from being torn from its connector the first time the actor moves or bends over, use a rubber band to provide elastic strain relief. Attach one end of the rubber band to the tip of the antenna. The free end of the rubber band can be safety-pinned to the clothing or taped in place (use medical tape on skin). Thus, the antenna can be maintained reasonably straight (a little bit of slack is okay) yet protected against damage.

The transmitter antenna can be run vertically up or down from the body pack. However, if the antenna trails downward, then the transmitter should be mounted in an inverted position to avoid making a loop in the antenna.The transmitter antennas can also be run horizontally, such as partially around the waist. However, in these instances, the receiver antenna may need to be tilted sideways (matching the angle) to improve reception.

Under no circumstances should the mic line and antenna wire ever cross. This will definitely reduce your range. Run the mic cable out from the body pack in the opposite direction of the antenna. When the transmitter is mounted on the body upside down (the antenna running downward), it is okay for the mic line to loop upward, as long as it doesn't cross the antenna.

Install a fresh battery in the transmitter every time you use it. It sounds like a detail that should be obvious, but all too often, radio mic problems boil down to a weak battery in the transmitter. Change the battery frequently - every four to six hours with most brands.

Forced Perspective:
There are a couple of ways to soften the problem of forced close-up perspective. The first is to select a lavalier with an open sound, such as the PSC MilliMic, Tram TR-50 or Sennheiser MKE-2, rather than a lavalier that tends to isolate, such as the Sony ECM-55. Another solution is to attach the lavalier a little lower on the body than usual. When there are two people playing close to each other, it sometimes helps to mic each person off of the opposite person's microphone.

Antenna Placement:
The antenna of the receiver should initially be adjusted to match the angle of the transmitter antenna. Then experiment with changing the angle, for sometimes an unusual condition on the set may favor an odd combination of antenna angles to yield best signal.

A clean line-of-sight between receiver antenna and transmitter is important, since almost any object or body can deflect or absorb the RF signal. Mounting the receiver up high, such as on a wooden ladder, usually helps.

Wireless mics come equipped with one of two forms of receiver antenna: the straight wire "whip", or the shorter helical "rubber duckie". The straight "whip" will yield the best reception, although the "rubber duckie" offers more convenience in terms of mobility.

There are some special antenna systems that can be used to improve reception. Directional antenna systems can be used to reject radio interference when the source is identified. High-gain antenna systems can significantly increase the range of most wireless mics.

Any time the receiving antenna is separated from the receiver, care in selecting low loss cable becomes important. 50W RG-58U is a standard cable, however it has significant loss especially at higher frequencies. Keep the cable length as short as possible, and select lower loss cable for longer cable runs and higher frequencies.

Placement and Environment:
Strive to maintain minimum distance between the transmitter and receiver. Move the receiver/antenna from shot to shot in order to achieve close and clean line-of-sight placement. Don't be afraid to locate an antenna just outside of camera frame, or even to conceal it behind a prop right in the shot or set itself.

Sometimes, it maybe expedient to have the boom person or third person physically carry the entire receiver during the take in order to maintain proximity with the actors. Given the option, it is better to run long lengths of audio cable (from receiver to recorder) than to have long lengths of antenna cable (from antenna to receiver).

Virtually anything can interfere with good radio transmission and cause bursts of static. Check for metallic objects of any kind, such as jewelry, zippers, coins, snaps, and keys. If you cannot eliminate the metal, then at least reposition the antenna on the actor.

Carefully look at the path of transmission between the actor and the receiver. Pay attention to lighting or grip stands that may suddenly have appeared. A new influx of crew members or spectators can also block the RF signal.

Examine the location itself. Check for additional electrical lines, especially coiled feeds, which can generate magnetic fields. Dimmers and special effects equipment (especially neon) are always a problem. Motors can produce interference: Be aware of golf carts, forklifts, camera cranes, automobiles, and kitchen appliances.

Video and computer equipment can create strange fields. Be aware of Steadicams and other camera mounts relying on high intensity video or radio-controlled camera functions.

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