Pass interference, on the broadcast. 15-yard dropout penalty. Automatic reshoot.

Dropouts, hash, fade, intermodulation, spectrum reduction, et al, are daily struggles to the wireless microphone user. Frequency coordination is exponentially more important today than even last year. We talk to customers daily who would benefit from a basic wireless technology primer, so here it goes.

The first thing you must know is the majority of wireless production microphone systems are in daily competition with television broadcasts. For example, if you have a Lectrosonics or Zaxcom wireless system in frequency block 21, you are competing with TV broadcast stations 25 through 29. This is also expressed as 537.600-563.100 MHz. When we say TV channel 25 remember this is in the airwaves, not cable or satellite. If you’ve got a TV with some rabbit ears and your watching UHF channel 25, then that is what you are fighting.

Secondly, lets talk about VHF vs. UHF. This is more than the 2 knobs on the old black and white Zenith in your basement. We often here the question “Is there a reason not to use VHF?” The answer is complex. VHF gear is not currently popular or being marketed by the major RF mic manufacturers. The advances in wireless audio quality have found themselves in the UHF world, but have not quite backed up in the lower VHF frequencies. VHF and UHF are two different sections of the frequency range spectrum. UHF gained in popularity among wireless manufacturers because it was generally more open. Less traffic. Ironically, much like my daily commute, going back to the surface streets (VHF) is becoming more and more reliable because everyone is on the interstate (UHF). Crazy enough as it may be, some of your old VHF Vega Dynex wireless in your storage shed may be some of the best sounding analog wireless ever made. The trouble is, few people work on it and parts are impossible to find. VHF uses lower frequencies. A lower frequency has a longer wave length, thus longer antennas. Lower frequencies also travel farther and through walls and surfaces better. UHF on the other hand bounces off of surfaces better and can “go around walls.” Both situations can be advantageous. UHF does have one slight edge over VHF. Power. The FCC does allow UHF to broadcast 250 milliwatts (mW) from the transmitter, VHF is limited to 50 mW. However, if you consider the Sennheiser Evolution and Audio-Technica 1800 transmitters output 30 mW this isn’t terribly scary. Here’s a small equation to find the difference in power output in terms of distance.

4(power output)= 2(distance)

For ease of numbers lets say your 50 mW VHF transmitter goes 100 foot. Then in order to double that distance, you need a 200 mW UHF transmitter.

You may expect wireless manufacturers to peer back in the VHF frequencies soon. UHF is getting slammed. The FCC has recently begun auctioning off sections of the 700 MHz frequencies. These UHF frequencies are also known as Lectrosonics/Zaxcom Blocks 27-31 (Block 27 starts on TV Channel 50). In early 2008, Sennheiser will discontinue their Evolution wireless in frequency group C. Group C covers 740-776 MHz.

In addition to these frequencies disappearing from television broadcast and wireless microphone usage, the digital television requirements of the FCC are picking up speed. Every television station must broadcast a digital signal by February of 2009. So they need frequencies to comply. What does all of this mean to you? Don’t panic, its cool.

REDEMPTION!

No, seriously don’t worry. Your best weapon around these competing broadcasts is knowledge. Many professionals are not using their gear to its potential. Let’s find a clean frequency. First of all, look at the chart above. The frequencies in red are not auctioned yet. The frequencies that have been auctioned haven’t necessarily gone live, they may not for years. That is very important. Just because someone owns it doesn’t mean they are using it. Most modern wireless microphones (Audio-Technica, Lectrosonics, Sennheiser, and Zaxcom included) have frequency scanners built-in. They are a huge help in finding that small slot in between the new wireless telephone technology and the public access station that has pledged the airways for years. In addition, Lectrosonics and Sennheiser have excellent frequency coordination on their websites. I’ll walk you through both shortly. If you really get in a jam, check the VHF frequencies in the area, you might find the glorious void your looking for, then check our consignment site, on any given week I receive 1 or 2 VHF Lectrosonics systems waiting for revival in production. Finally, remember all of those TV stations going digital? Eventually, they will no longer broadcast analog. This means all of their former analog transmission frequencies will be free, until the next thing fills them up.

How to use the Lectrosonics TV station lookup…

1. Click here.

2. Choose your city, for multiple cities hold down Ctrl (PC) or Command (Mac) while selecting.

3. Scroll till you find your block.

4. Open TV stations (AKA usable frequencies) are shown, as well as television stations broadcasting in the area.

5. Use the key. If no open stations are shown, look deeper. The chart assumes you are standing in the exact center of the city. If you see nothing open, but A52S, you still may be fine. Here’s why. A=analog broadcast, D=digital broadcast. The number indicates a mileage and the final letter a direction. So A52S means an analog station is broadcasting 52 miles due south of the exact center of the city. You are already 5 miles west of the city. Let’s go to Pythagoras. 52 squared + 5 squared =2729 otherwise known as C squared. The square root is…………..FAR ENOUGH AWAY TO WORK. Let’s face it most any television broadcast more than 30-35 miles away should be workable.

Sennheiser’s new improved frequency finder…

1. Click here.

2. Enter the Zip Code of your production location.

3. If you know the corresponding TV broadcasts to your wireless enter the start station and end stations. If not leave them be.

4. At first, select usable channels. Then you can see which frequencies are open.

5. If nothing is open, check the occupied channels. The same rules apply as far as mileage as the Lectrosonics chart.

6. Then you have the added advantage of selecting the wireless unit of your choice (Sennheiser models only).

International?

Each country has their own stipulations on wireless microphones. Finding information about available frequencies can be very hard. One website that can be helpful is www.tvradioworld.com. This site allows you to select a country, if your lucky a city, and if your very lucky, what frequencies are used in that city. You may also find info on legal frequencies and transmission power.

United Kingdom? Try This.

Vancouver B.C./Washinton State? Analog broadcasts. Digital broadcasts.

The RF spectrum will continue to change, your best weapon is knowledge of how to use it in the first place. Till next time.