So a side question... and yes I realize if I spent more time in the audio forum and a little less time in the lighting forum I would probably know the answer... I've heard that some frequencies are going to be sold off from the spectrum and it could
effect some wireless gear. What frequencies are they and is that something I need to be concerned about when making this
purchase?
First, some background. The FCC is in the middle of what is called Rebanding," which means they are reorganizing who can use what parts of the radio spectrum. This is occurring in numerous parts of the radio spectrum, but primarily in the 2 GHz, 800 MHz, and 700 MHz bands. As you may know, the
UHF TV part of the spectrum used to span from 470 MHz to 806 MHz (
channel 69). Because of the demand for
clear frequencies for public
safety radio traffic, the FCC is reallocating the upper part of the 700 MHz band from TV to land-mobile communication. Essentially, this means we can no longer continue to operate illegally in that part of the spectrum, because the interference generated by our wireless mics will be much more serious.
This is not the only problem we
face. With the advent of digital television, we are losing valuable spectrum in which we can operate. This is because a digital signal takes up the entire six megacycles allocated to it, while an analog signal had three major peaks within it (between which we could operate if we had to). Additionally, there is a bill in congress promoting the opening of the frequencies allocated for TV stations but not actually in use to consumer devices such as wireless
network devices. This is problematic for us because there will be no way to predict the interference that these units may cause. There is another bill in congress which would protect us from this, but it's currently sitting in committee (write your congressperson now!)
The solution to these problems is complicated. First, we must invest in equipment which is able to cut through the noise. This does NOT mean we need more powerful transmitters! We need better antennas and better receivers. As far as antennas go, it is a good idea to invest in directional antennas with high
gain. These antennas should be positioned so that they are pointed AT the
stage and AWAY from powerful TV transmitters. They should also be as band-limited as possible. Those antennas that are "wideband" will not help you; they'll just
pick up more garbage. If the distance between the receiver and antenna is more than a few feet, invest in quality RG-8X coaxial cable and use quality terminations (N connectors where possible; otherwise
BNC. Absolutely no F,
RCA, PL-259/
UHF, or otherwise!).
Along with quality antennas, the second part of the solution is quality receivers. Sorry to say it, but the $299 wireless systems that manufacturers make will NOT cut it! You need to
purchase receivers with quality front-end filtering if you want your mics to work. This means you need to be looking at receivers OVER $500 per
channel. This doesn't include the transmitter. You should be also able to tune the receiver at 100 kHz steps or better (smaller). Units which have "
preset" channels or which do not have a display are not worth even looking at, especially if you live near a city.
It is important to consider how your antennas will connect to your
system as well. When buying systems, you must be sure to include in the price the cost of antenna filtering and distribution. In many cases, you will need multiple distributors, each of which can cost as much as a receiver. They also take up space in the rack. Lectrosonics is the exception to this rule - they include onboard filtering, splitting, and amplification in their
VENUE receiver systems. However, as I said above, this is limited to a 50 MHz band of frequencies, so if you have a particularly large
system (>24 units) or a lot of RF in your area, you may need to set up multiple antenna sets to
cover all of your units, or split them out beforehand with a
passive splitter.
Finally, be sure to stay
clear of units which operate in the 700 MHz band. When you order a
system, work with your vendor to select frequency bands which have the least amount of interference in your area. Also, determine if your vendor can do frequency coordination for you. If so, they should make a site visit, run some tests, and come up with a list of frequencies you can use. If not, you'll need to figure out what TV stations are in your area and draw up a list of frequencies. I've posted on how to do this before; please search the archives for more.
Does this
clear things up a
bit? Please let me know if you have any questions (PM is fine too!)