By Wayne Connors
By and large, a microwave RF link uses the same kind of equipment as a more traditional mast-type RF link system, such as MF and HF and Wi-Fi. The main differences lie in antenna construction and the frequencies used. Microwave transmissions utilize much higher frequencies than other types of radio systems, normally in the Ultra High Frequency and Very High Frequency ranges. Some microwave systems utilize even higher frequency ranges. There are numerous advantages and drawbacks to using microwave technology in the RF links you use.
There are two main types of antennas for long distance RF signal propagation. The oldest type, more suited to straight voice transmission and used by MF & HF radio stations is the tower-mounted mast antenna. The higher the end of the antenna is, the longer the range for a given transmitter output strength. This type of antenna propagates the signal in a complete circle around the tip of the antenna. Signal aiming is achieved using microwave RF links. These are a dish-shaped receiver, with a high gain amplifier and collector at the focal point of the dish. This type of antenna provides for fairly secure line-of-sight signal transmission over long distances and is great for connecting to buildings to the same network wirelessly. Because the signal is highly focused, microwave RF is capable of being transmitted over longer distances and can use satellites to transmit signals cross-country or across oceans.
Frequency Spectrum of microwave RF Links
For the most part, RF links that utilize microwave antennas operate in the Very High Frequency and Ultra High Frequency ranges. VHF is the lower frequency range of the two, encompassing frequencies between 30 Megahertz and 300 Megahertz. These frequencies are ideal for low-bandwidth requirements, such as smaller MAN networks. With higher bandwidth MAN networks, higher frequencies are required to keep up with the throughput needs. These can include the 300 MHZ to 3GHZ UHF range or even higher Super High or Extremely High Frequency ranges.
Advantages and Drawbacks of Going Microwave
If your network needs to encompass users in a number of buildings throughout a city, and you want to cut down on the number of eavesdroppers, using microwave RF links is a good choice. You get more distance than a standard mast antenna and you get line-of-sight transmission, so any receivers not in that line of sight won’t be able to pick up your signal. However, if there is another building obstructing that line of sight, the signal will be blocked. Properly aiming a microwave antenna will make the difference between having a network connection and not having one; special equipment is available for this. Obtaining optimal signal strength at the receiver is almost as much art as science.
There are a number of considerations when deciding on a type of antenna system to use, whether you’re creating a Wide Area or Metropolitan Area Network, or even creating a neighborhood television studio.
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