Additional bands used by wireless microphones include the “944 MHz” band between 944 - 952 Mhz. This is a band reserved for use exclusively for broadcasters.

Also, the “ISM” band between 902 - 928 MHz is an unlicensed band used by several wireless microphone products. Finally, the 2.4GHz band is another unlicensed area used by wireless manufacturers.

Although the UHF TV band classically extended up to channel 69, channels 52 to 69 (698 MHz to 806 MHz) has been converted to non-TV use - divided up by the U.S. government/FCC and auctioned to various companies for wireless devices available on the consumer market.

Accordingly, it is now against the law to use wireless microphone systems in this band. Even though a system has operated in this range without problems for years, it is illegal.

With all these competing signals in the air throughout the VHF and UHF bands, even high-quality wireless systems can run into problems when operating at distances of 100 feet or less between the transmitters and receivers.

Range problems usually appear as “fizzing” or “swishing” noises, perhaps followed by the complete loss of the audio signal. (This is called dropout.)

In addition to the low transmitter power, two other problems can limit the range of wireless systems. The first is signal absorption due to building construction and internal equipment, or shielding by metallic objects such as electrical wiring, air conditioning ducts, storage cabinets and the like between the transmitter and the receiver.

Note the dual antennas on this wireless receiver, indicating it uses diversity.

The term “line of sight” is often used to express the idea that the signal path from the transmitter to the receiver should be open and clear of obstructions.

This simply means that if the wireless user can physically observe the receiver antenna, RF signal absorption is likely to be low.

The second problem is called multipath. It’s a phenomenon that results in numerous small areas where little or no wireless signal is present because of reflections and the resulting phase cancellations, and it often tends to occur within a fairly short distance between transmitter and receiver.

To overcome the problem, a majority of modern wireless receivers now use a technique called diversity. With diversity, two slightly separated receiver antennas are used, making it very unlikely that both will simultaneously be in one of the low signal (multipath) areas.

The receiver automatically selects the antenna with the strongest signal, not only solving multipath, but also increasing the reliable range of a wireless system.

A final note: most users are surprised to learn - despite urban myths to the contrary – that the U.S. government requires wireless systems to be properly licensed prior to use. 

Unfortunately, the agency in change of issuing these licenses (Federal Communications Commission, or FCC) makes it very difficult for conscientious users to actually comply.

As a result, the vast majority of users don’t go to the trouble. But keep in mind that unlicensed wireless systems are in technical violation of FCC rules, and therefore are theoretically subject to fines.

As a practical matter, the FCC has neither the resources nor the inclination to go after the “average” wireless user, so the risk is low. But not zero. Due to the recent changes in spectrum allocation, this issue is being re-visited.

It appears that the FCC may make it easier for typical wireless microphone users such as churches, theaters, musicians, etc. to register their products.

This would also be beneficial in the event that additional types of consumer devices appear and complete for the same spectrum we are currently using.

Click here to continue to Part 2 (Avoiding Wireless System “Issues”) of this series, or click here to go directly to Part 3 (Downsides Of Digital).

Page 3 of 10
Previous  « First < 1 2 3 4 5 > Last »  Next