Harmonic filters

All RF transmissions create harmonic and sub-harmonic tones. They are like reactionary waves.  A visual example would be waves on an ocean.  Sometimes two or more waves can come together to create a larger wave, or even cancel each other out.  The problem in wireless systems is when a harmonic overtone lands right on or very near the same frequency that another wireless system operates on. This type of problem typically occurs when more than one wireless systems are used together. Lower priced wireless systems are typically designed without filtering to handle these issues simply for cost reasons.  If you want to use more than a couple wireless systems together, and want to spend under $150.00 per unit, you are asking for trouble… don’t say I didn’t warn you…

C) Grounding

An antenna needs a good ground. This is especially important for non-diversity receivers. Ever take the ground wire off of your stereo antenna? If so, you know why a ground is needed. Cheaper wireless models use the circuit board for a ground, because the housing is typically plastic. The circuit board has about as much metal in it as a gym shoe.  Circuit boards are laid in gold about a ba’zillionth of an inch thick. You need metal mass for a good electrical ground. The tiny amount of metal in the circuit board is simply not sufficient for a good ground. Plastic case units that don’t have a grounded electrical cord are fine (still not as good as diversity systems) as long as they have the much-needed second antenna to act as the ground. They are not rabbit ears like your granddad’s TV set used to have. They need to be perpendicular to each other--one straight up, the other 90 degrees to the side. The manual will tell you which one is the ground and which one is the reception antenna. This added antenna makes a huge difference in the quality and reception in a non-diversity system.

3) Operating Band - UHF vs VHF

Wireless microphones work typically in two bands. VHF and UHF.

VHF operates typically in the range of 169.5 - 213.8 MHz (Megahertz)

UHF operates typically in the range of 650.1 - 951.9 MHz (Megahertz)

First, the most noticeable difference between UHF and VHF is sound. If you had two really good systems, one being VHF and one UHF, the UHF typically should sound better. Why is that? VHF systems compress the signal before transmitting. UHF does not. Since UHF is not compressed, it gives a much more natural sound.

As you can see from above, UHF is a much higher band, and also offers a much greater range of frequencies. UHF is unquestionably the better choice with very few exceptions.  Extreme care and planning is required of a dealer (especially mail order) to select the right frequency for your area it will not be interfered with by your local TV broadcast.  Not all frequencies work in all areas.

4) Single or multi-channel systems

Will this wireless work in my area? What if I travel to another area?

a) Single channel systems are just that; you have only one channel. If you go to your show, meeting, or venue and your wireless is not working well and you tried moving it around and put in a fresh battery, guess what? You have to live with it. I am not trying to discourage you from buying a budget system, or a single channel system, but those are the facts. There is not a lot you can do. Move it around, and try your hardest to make it work, but you can’t change the channel or the airwaves. There was once a pastor of a church in Winchester, Indiana. Somewhere near the church there was a group of teenagers that liked to talk on their dads CB radio when he wasn’t home.     One Sunday morning the congregation briefly heard words that one would not expect to hear in church coming from their wireless system.  The wireless system channel was over driven by the CB radio harmonics as a result of the booster and the wireless was VERY quickly shut off. It was a budget-priced, single-channel, non-diversity VHF system that was soon upgraded.  Interference will happen to any wireless at some point in time if you use it enough. Once again, NO wireless is foolproof!  Some are just far less likely to have problems than others.

Mail order Warning

  The manufacturers select the optimum frequencies to work within the area of the store so that they have units to sell that should work fine to their market.  Not all wireless channels work in all areas. See where this is going?  Let’s say you find a great wireless system from John Doe's Super Mega Music.com. You call or click to order it and wait anxiously while John Doe’s guitar salesman grabs one from the counter and ships it. You receive the unit just in time for your big even, and it does not work!  So you box it up and send it back.  John Doe calls you a week later and tells you that you are nuts, and that it works fine.  Guess what?  You both are right. The frequency was selected for “his” area, not “yours”.  Retailers traditionally never had to deal with frequency issues before.  With the internet changing the way we do business, that has all changed.  The frequency problems resulting from new wireless e-tailers popping up are both the fault of the stores and the manufacturers.  A complete understanding of wireless systems is essential to properly sell and service wireless customers. Before any wireless system is shipped or even picked off the shelf, your zip code should be entered into a special computer program that is kept up to date with the FCC registered broadcast charts. This program should cross-reference your zip code against any possible interfering broadcast frequency in your area. Also if you have existing wireless systems, you must let the retailer know. These frequencies should also be entered into the computer program to cross reference for harmonic interference as well.

b) Multi-Channel systems are far superior to single channel units for obvious reasons above, however, there is more to know than you might think.  Multi-channel or “Frequency Agile” systems permit the user to change the channel on the transmitter and receiver. There are often many channels to choose from. A multi-channel system can have as few as 10 and up to a more than a thousand channels.  These systems are capable of avoiding long-term frequency interference issues.  . They are more suited for the person who is traveling between large metropolitan and broadcast areas. Caution! Don’t be fooled into thinking that the more channels it claims to have, the better it is.  This is not always true.  First you must know the difference between one channel and the next.  In other words, how far apart are the channels?  If 4 or 5 channels are skipped just to get enough separation, then you really are not getting what you think.   You can take 650.000 and 651.000 and divide it into 1000 different channels if you like, however, you would likely only get 4 usable channels.  (0.100 MHz to 0.125 MHz would typically be a safe usable increment between channels). Make sure you know how many you can actually use together.  For example a 200-channel unit typically would yield about 10-15 simultaneous frequencies.  There are very clear benefits to buying a frequency agile system.

c) Multi-channel scanning systems are the top of the line. These are systems that will scan the airwaves and select the cleanest possible frequency in which it can operate. They are the same as the above multi-channel systems, but they do the work for you. They take the guesswork and trial & error out of the picture. They take into account what is actually happening in the airwaves, rather than what should be there based on textbook data. These systems are obviously more expensive, but suit the needs of wireless users who seek the cleanest and clearest reception for their application. Technology has rapidly advanced and now units like these can be purchased for hundreds, rather than thousands of dollars just a few years ago. These systems are recommended for those who use the system on a regular basis and when it is important that your message or performance is heard clearly and uninterrupted.

What’s happening recently in the airwaves

There are many people using single channel wireless systems that bought them in the past 1-5 years calling us for service.  An unfortunate situation is that all to often their system is just fine, but no longer usable.  You see, the system they are using did not change, but rather the environment they are using it in did.  The airwaves are being blasted with wireless internet, cell phones, and a new enemy… digital television.  The FCC has been issuing broadcast permits at an unprecedented pace.  Most television stations broadcasted in the analog realm up until a few years ago.  Today they are changing over to digital broadcast.  The difference is the bandwidth they use.  An analog broadcast takes less bandwidth.  The transition to digital broadcast instantly wipes out once usable wireless microphone frequencies.  The unfortunate situation is that there is nothing you can do about it.  Wireless microphones are permitted to operate only as long as they do not interfere with public communication broadcast.  You can’t compete with the TV industry.  Compared to the likes of Ted Turner, the wireless industry as a whole is but a lemonade stand.  The problem is only getting worse. I strongly suggest to those considering wireless to go with UHF Frequency agile systems whenever possible.

New technology…. What’s to come?

There are now PC driven systems, and interlinking systems that will scan the airwaves and set the complete system up for you in a multi-system application.  You still have to set the channel manually on the body packs, but that technology is rumored to be in prototype now. 

Wireless microphone technology is giving artists the mobility to express their message or their art with total freedom.  No longer must we be tied down by the reach of a “cable”.  With a little good purchasing sense, and proper use, wireless microphone technology can give you the freedom you have dreamed of; even on a limited budget.