Outdoor/Indoor mounting considerations
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RF Cables
Connectors
Splitters
- Improper installation or selection of cables can detrimentally affect the RF communications more than just about any other component or outside influence.
- Make sure you select the correct cable.
- The impedance of the cable needs to match the impedance of the antenna and transceiver.
- If there is an impedance mismatch, the return loss from VSWR will affect the link.
- Make sure the cable you select will support the frequencies that you will be using. Typically, cable manufacturers list cutoff frequencies, which are the lowest and highest frequencies that the cable supports.
- This is often referred to as frequency response. For instance, LMR cable is a popular brand of coaxial cable used in RF communications.
- Cables introduce signal loss into the communications link. To determine how much loss, cable vendors provide charts or calculators to assist you.
- The better cable is typically thicker, stiffer, more difficult to work with, and of course, more expensive.
- For example, 100 feet of LMR-400 cable used on a 2.5 GHz network (2,500 MHz) would decrease the signal by 6.8 dB.
- LMR-1200 will not work with 5 GHz transmissions. LMR-900 is the highest you can use.
- You can use LMR-1200 for 2.4 GHz operations.
- Attenuation increases with frequency. If you convert from a 2.4 GHz WLAN to a 5 GHz WLAN, the loss caused by the cable will be greater.
Connectors
- Many types of connectors are used to connect antennas to 802.11 equipment.
- Part of the reason for this is that the FCC Report & Order 04-165 requires that amplifiers have either unique connectors or electronic identification systems to prevent the use of noncertified antennas.
- This requirement was created to prevent people from connecting higher-gain antennas, either intentionally or unintentionally, to a transceiver.
- An unauthorized high-gain antenna could exceed the maximum equivalent isotropically radiated power (EIRP) that is allowed by the FCC or other regulatory body.
- In response to this regulation, cable manufacturers sell pigtail adapter cables.
These pigtail cables are usually short segments of cable (typically about 2 feet long) with different connectors on each end. - They act as adapters, changing the connector and allowing a different antenna to be used.
- Many of the same principles of cables apply to the connectors as well as many of the other accessories.
- RF connectors need to be of the correct impedance to match the other RF equipment.
- They also support specific ranges of frequencies. The connectors add signal loss to the RF link, and lower-quality connectors are more likely to cause connection or VSWR problems.
- RF connectors on average add about 1/ 2 dB of insertion loss.
Splitters
- Spliters aka signal splitters, RF splitters, power splitters, and power dividers.
- A splitter takes an RF signal and divides it into two or more separate signals.
- Only in an unusually special or unique situation would you need to use an RF splitter.
- One such situation would be if you were connecting sector antennas to one transceiver.
- If you had three 120-degree antennas aimed away from a central point to provide 360-degree coverage, you could connect each antenna to its own transceiver, or you could use a three-way splitter and equal-length cables to connect the antennas to a single transceiver.
Reference:
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
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