Rod Reilly wrote: ". . . make sure the antenna . . . runs vertically rather than horizontally."
This is not entirely true. For optimal reception of the radio signals from the microphone transmitters it is suggested that the two diversity antennas be oriented orthogonally to each-other (See? Geometry class applies to theatre!) and the plane of the orthoganality is perpendicular to the performer's transmitters (i.e. tilt the set of receiver antennas so they are aimed at about waist high near mid-stage).
This means that if you have two whip antennas (omni-directional types) (http://www.electrovoice.com/product.php?id=987) and you are standing on the stage looking at them they form a separated 'V': ╲⃔ ⃕╱ where the two lines appear perpendicular to each other (i.e. splayed ±45° from vertical or 90° between them).
Similarly, if you have two directional antennas (log-periodic antennas, sometimes incorrectly called 'yagi antennas')(these antennas usually look like flat trapezoids - Dang! There goes that geometry class again!) (http://en-us.sennheiser.com/a-2003-uhf) where the narrow end of the paddle is pointed towards the performer's waist near mid-stage, then the performer sees: ╲⃔ ⃕╱ where the two lines appear perpendicular to each other (i.e. the front edge of the paddle that is visible is splayed ±45° from vertical or 90° between them). (Cavaet: The exception to this rule is the Sennheiser paddle-shaped omni-directional antennas (http://en-us.sennheiser.com/a-1031-u) -- which should be set-up with the flat side facing the performers - perpendicular to them and then tilted apart ±45° (i.e. 90° between them) - it looks like a pair of tall skinny playing cards that are tilted one left, and one right.)
What this does is create Phase Diversity. As performers move around, hold hand-held mics in different positions, or if an actor lies down or leans at an angle, the odds are that one of the two antennas will get a radio signal that is oriented near the same direction. If both antennas are mounted vertically, then each has a good chance of receiving a signal transmitted from the performer with the vertical antenna, and both have a bad chance of receiving a signal from the performer with a horizontal antenna.
Why do I mention this (other than to drive every one nuts)? Sometimes it is more convenient to place an antenna horizontally or diagonally than it is to place it vertically. This is costume specific.
Another example is in a musical performance where you have a performer with a wireless instrument mic (i.e. a guitar player). If the guitar strap is diagonal across their back, and the transmitter / antenna is attached to it, then when they face the receiver antennas the transmitter antenna is aligned with one of the receiver antennas and orthogonal (i.e.a bad match) to the other receiver antenna; yet when the performer turns around and faces upstage, then the transmitter antenna is now aligned with the other receiver antenna and orthogonal (i.e. bad match) to the first. This way there is always one receiver antenna with a better signal and the other receiver antenna with a 'not so good' signal.
Similarly, if you have performers holding handheld wireless mics, they typically hold them at about a 45° angle to the ground. If they turn right, then one of the receiver antennas gets them, and if they turn left, the other receiver antenna gets them.
Of course, there is never a silver bullet with wireless mics - there are too many variables.
Basic things that will help are:
- Always use fresh batteries for a performance (never trust a used battery - Don't ruin a performance for the sake of a few dollars worth of batteries).
- Space your diversity antennas apart (10-15' is recommended - the 18" of a rack mount doesn't really provide the spatial diversity needed)
- Splay your antennas for phase diversity (see above).
- Don't mount your antennas inside a metal rack.
- Don't mount your antennas on the face of a rack panel in the receiver rack (despite of the fact that wireless mic manufacturers put holes there and tell you 'everything is going to be OK").
- Don't mount a bunch of antennas next to each other and create an "antenna farm". Antennas need to be 12-24" away from any other metal objects to do their job best. 'Other metal objects' includes metal wall studs (hidden inside sheet rock walls), conduits (hidden inside walls), plumbing pipes (hidden inside walls), steel rebar rods (hidden inside concrete walls), ceiling tile grids, aluminum or steel window frames, stage rigging battens, handrails, steel equipment racks, etc. If you have more than one wireless mic, then buy an antenna splitter (or more than one for larger set-ups) and just use one pair of antennas to feed all of the receivers. You will need separate antennas and splitters for VHF, UHF, 900 MHz, and 2.4GHz band systems. All of these frequency bands are becoming more common and are sometimes intermixed just to to get enough open frequencies that will work together without interference from other local radio signals. Don't forget that there may be wireless mics in classrooms, gymnasiums, dance studios, football stadium, and maybe a nearby church, so you have to coordinate all of these frequencies if there is a chance that they might be used at the same time you are rehearsing or presenting a show.
- Mount your antennas high enough that they can have a direct line of sight between the transmitter antennas and the receiver antennas. Humans are 98% water and they absorb Radio Frequency energy A LOT. The more bodies between the transmit and receive antennas, the less radio signal that will make it to your receivers.
- Check to see that all of your transmitters are set to a similar range of transmit power (25mW, 100mW, 250mW, etc.). If a few of them are set to a high transmit power and the others set to a lower transmit power, then it may make it difficult for your receivers to pick-out the correct signal information and provide good sound. Generally speaking, more power is not better. Unless you are in a football stadium and hundreds of feet away from the transmitter, there is little reason to "crank it to 11" with the RF power.
- Use the commonly available frequency selection tools to find a set of coordinated frequencies for your wireless devices. Regardless of if you have 3 or 30 devices, if you have even one device that it is not coordinated, then you run the risk of numerous other channels misbehaving. ALL of your devices must be frequency coordinated as a set. If a new performer brings their own wireless transmitter / receiver for a guitar or saxophone, then this one item could mess-up your whole show unless you have it entered as one of the devices in the calculation of a set of coordinated frequencies.
Final Note: Be aware that the FCC has just agreed to auction-off the 600MHz-700MHz frequency band over the next couple of years. Just like they did with the 700-800 MHz band a couple of years ago. You need to check the operating frequencies of your equipment and start to budget for replacements before the hammer comes down. Be VERY wary of salesmen trying to offer you "good deals" on wireless mics and IEM systems - Triple-check and get it in writing that the equipment does not operate in the 600 to 800MHz bands - as there are unscrupulous people out there that are going to be dumping this gear at bargain-basement prices.
Some products can have the transmit / receive frequency changed by the user, some can be done by the factory, and some cannot be changed. Donate unusable equipment to foreign missionaries (let the frequencies be their problem in whatever country they are traveling to) or dispose of them at an appropriate electronics recycling depot. Think Green and don't just dump it in the dumpster.
------------------------------
Erich Friend
Theatre Consultant
Teqniqal Systems
Original Message:
Sent: 04-04-2016 09:17
From: Rod Reilly
Subject: mics
Erich is correct - pockets and belts for transmitter packs saves lots of damaged transmitters and many times more damaged cables caused by the stretching that occurs when the pack falls and the mic stays attached.
While we have no where near as many variants as Erich's preferred vendor, we do make belts in 2 lengths and 2 colors (no white_ just black and taupe. http://www.bodymics.com/storage.html These start as low as $16 each in quantity (25) - about $20 each in singles, $57/3 pack, $180/10 pack, $400 in 25 packs. We can mix and match sizes and colors in any pack and still give you the pack price, but you will have to contact us directly. The standard single color, single size packs can be ordered on line or by contacting me.
Our belts firmly hold all normal size bodypack transmitters from "all" manufacturers. The mini packs from Lectrosonic and Shure (and others are not recommended for use with these.
Remember Erich's advice - make sure the antenna is unencumbered and runs vertically rather than horizontally.
------------------------------
Rod Reilly
Owner, Bodymics
908-899-1277
Somerset NJ