UHF Versus VHF
The mistaken idea that UHF wireless systems somehow have overwhelming inherent advantages over VHF systems is widespread. However, the facts simply do not support this notion. As is the case with many technical issues, there are both advantages and disadvantages to UHF, as there are for VHF. Accordingly, in a particular situation, UHF may, or may not, be the best choice.
There are a number of important factors to consider. These include where the systems will be used, how they will be used, and for what purpose or application. Cost is always a concern and invariably plays at least some part in the final decision. Other factors, such as whether the equipment will be used in many different cities, may also be important. Only by considering the entire situation can an informed choice be made.
Simply put, UHF systems do not hold any large technical advantage over otherwise similar VHF systems. The primary advantage of UHF operation is that there is less chance of interference because of more available frequency spectrum.
Interference due to spurious outputs from other radio frequency equipment is somewhat less of a problem at UHF frequencies because there are fewer transmitters operating at frequencies likely to cause problems. Interference due to electrical equipment, digital devices, computers and other electronic equipment is also generally lower at UHF frequencies. This is because noise from these sources becomes less intense as the frequency increases. Interference of all types does not travel over as great a distance as at VHF frequencies.
UHF wireless systems always cost more than similar VHF wireless systems. The extra cost of UHF equipment is due to the necessity of using more expensive ultra-high-frequency parts, the greater total number of parts required and the need for more expensive construction techniques. Other manufacturing costs are also higher, especially the amount of time required to adjust the equipment and verify its performance. While the cost difference between UHF and VHF equipment has been declining, it is unlikely to disappear.
Battery life for VHF wireless transmitters is almost always better than for similar UHF units; over the life of a system the savings in battery costs can be very significant. For larger wireless installations, the cost of antennas, cables, antenna splitters and preamplifiers is usually much less for VHF systems and performance is generally better.
As can be seen, cost considerations tend favor the use of VHF systems, while UHF systems are less likely to suffer interference. However, there are several other applications issues that can affect the choice:
- Whether the choice is UHF or VHF, diversity systems are highly recommended. Diversity is especially valuable for UHF systems because dropouts due to multipath are more troublesome at UHF frequencies.
- If the wireless equipment will be operated in the central parts of a major city, or in a heavy industrial area, UHF might be a better choice due to possible interference at VHF. However, entirely satisfactory VHF operation can still be achieved if frequencies are carefully selected and interference from industrial equipment is avoided.
- If the wireless equipment will be used in different cities, VHF systems operating on the special frequencies in the 169-172 MHz range will be a good economical choice (applicable in U.S. and Canada). However, these frequencies, which are sometimes referred to as "traveling frequencies," are very popular, and are not a good choice for situations where large numbers of wireless systems are likely to be present, such as at trade shows and expositions. In such situations, frequency-agile UHF systems will be a better choice.
- Fixed-frequency (single channel) VHF and UHF systems in the TV bands may not be good choices for traveling use. This is because all VHF and most UHF TV channels are used in one location or another, and frequency conflicts will eventually occur. Frequency-agile UHF systems will be a better choice.
- If the wireless equipment will be used in situations where several other wireless systems are likely to be present, UHF systems are recommended. This is because more frequencies are available, reducing the chances of interference.
- UHF systems are good choices in situations where the smaller and less-visible antennas are highly important, such as when the transmitters must be concealed on the body. UHF may also be preferable if high-performance antennas must be used to extend range.
In summary, there are a great many situations where VHF systems will provide excellent performance at substantially lower prices than for comparable UHF systems. However, there are certain situations, such as when interference is likely to be a significant problem, where UHF systems are the logical choice. Obviously, not all situations have been covered and there may be complications of one sort or another, or other factors that must be considered. If you are still unsure regarding the best choice for your particular application, please contact your dealer or Audio-Technica for further assistance.
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