I'm new to wireless field and have a question regarding RF math. How do I obtain the dB gain/loss of cables and...
antennas? Cables and cable connectors induce signal loss, while antennas are designed to introduce signal gain. These products cite a loss or gain rating in product specs. A loss of -3 dB cuts power (mW) in half, while a gain of +3 dB doubles power. A -10 dB loss reduces power to one tenth, while a +10 dB gain increase power ten times. The actual formula is ( Pdbm = 10logPnW ), but using 3's and 10's can approximate signal gain/loss without a logarithmic calculator.
For example, suppose you have an AP that outputs 100 mW. The first -3 dB connector cuts power in half (50 mW). The second -3 dB connector cuts power in half again (25 mW). A +6 dBi antenna doubles power twice (25 x 2 x 2 = 100 mW). Cable loss, typically rated in dB per 100 feet, must also be factored in -- as must any amps, attenuators, and splitters in the path between the AP and antenna. The result of this equation is known as Equivalent Isotropic Radiated Power (EIRP): the power output at the antenna. Remember that there is also Freespace Loss introduced as the signal propagates through the air between the sender and receiver.
Related Q&A from Lisa Phifer, Wireless Networking Expert
Wireless expert Lisa A. Phifer explains to what extent WEP cracking remains a worrisome issue. It all depends on your company's WLAN security policy.continue reading
Wireless expert, Lisa Phifer explains that it may not be worth enhancing Wi-Fi ad hoc mode since Wi-Fi Direct is a better alternative for enabling ...continue reading
Wireless expert Lisa Phifer responds to a question regarding a Mi-Fi and Android smartphone mobile hotspot comparison. She provides an in depth ...continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.