Product Focus

Line Isolation UPS Power Protection

Did you know that there are two fundamental types of Uninterruptible Power Supplies: Fail-Over and Line Isolation. The Fail-Over style is what you would normally buy at your local computer store to protect your home computer. This style of UPS provides surge protection and, when the power fails, an electrical relay switches the battery into the circuit (in just a few milliseconds.) A Line Isolation UPS (also called a "Double Conversion" UPS) converts the line voltage to DC, feeds through the battery, and then converts the DC back into AC 100% of the time. The output voltage is always a perfect sine wave and the protected equipment is 100% isolated from the input power line.

Although a Line Isolation UPS is slightly more expensive than a conventional Fail-Over model the added protection against power surges is well worth the price when it comes to protecting sensitive outdoor wireless radio equipment that might need a man-lift to service it if were to be damaged during a lightning storm.

Please contact Connect802 Sales at 925.552.0802 to learn more about Line Isolation UPS protection. We look forward to hearing from you!

Essential Wi-Fi

Frequency and Wavelength

Electrons moving in a wire generate an electromagnetic field. This field will cause electrons to move in other wires. That’s how radios work. It’s a simple concept, but the details are complicated. If we design the wires so that they are particularly good at transmitting and receiving these electromagnetic fields, then the wires are called antennas.

Any time-varying current will generate electromagnetic radiation. Microprocessor clocks and the digital circuits that they drive turn all of the wires in your computer into a radio transmitter. The current flowing in power lines running your toaster and lights generates plenty of radio waves, as you’ll notice if you try to use an AM radio near them. Even the ultra-low power 32kHz crystal in a wristwatch will radiate on the order of a picoWatt to a nanoWatt.

Electromagnetic waves, or radio waves, travel at the speed of light, c=~300,000km/s. The wavelength l of a radio wave is determined by the frequency of its oscillation f by the formula

c=f l

Example: What is the wavelength of AM and FM radio signals?

A: The AM band extends from 500 kHz to 1,500 kHz. 500kHz corresponds to l=3x10^8m/s / 5x10^5 cycles/sec = 0.6x10^3m/cycle, and 1,500kHz is 3 times shorter, at about 200m.

The FM band is from 88MHz to 107MHz. So FM signals have a wavelength of about 3x10^8m/s / 10^8 Hz = 3m

 Technology and Engineering

Optimal Antenna Size

An ideal dipole antenna radiates maximum power perpendicular to its axis, and zero power along its axis.

G dipole = 1.5 sin 2( q)

A good dipole can be made from two pieces of wire that are approximately one quarter wavelength each, yielding an antenna that is approximately l/2 long. Since these wires can be made fairly thin (until their resistance becomes comparable to the radiation resistance of the dipole, which is on the order of 50 Ohms), the area, volume, and cost of this type of antenna can be quite small as well. Such antennas can be printed on plastic with low-cost manufacturing techniques, yielding individual antenna costs of pennies or less in high volume.

For some applications, it is not the volume of the antenna that matters, but rather the largest dimension. If you need to swallow an antenna, you’re less interested in the fact that a printed-film dipole is only a fraction of a cubic centimeter than in the fact that it’s maximum length is 6 cm.

Resonant antennas can be made to be a small fraction of a wavelength in every dimension while still maintaining excellent performance, but this requires that they operate over a small fractional bandwidth. Fractional bandwidth is the frequency range of interest divided by the maximum frequency in the range, Df/f. For example, the 2.4GHz ISM band in North America extends from 2.4 to 2.485GHz, for a fractional bandwidth of 0.085GHz/2.485GHz or about 3.4%.

The size limit is

Df/f h = 2 (2 pd/ l) 3

where 2d is the largest dimension of the antenna, and h is the efficiency. As the antenna gets smaller, the product of fractional bandwidth and efficiency decreases dramatically.

Another problem with shrinking the size of resonant antennas is that their performance becomes very sensitive to the materials near them. Datasheets from companies that sell chip antennas show impressive performance as long as their reference designs are used, where a l/10 antenna is placed on a ground plane measuring l/2 square! Often the performance of these antennas degrades by 10dB or more under less ideal mounting conditions.

Web Searching: The Connect802 Web Presence [LINK: #presence]

At Connect802 we're your PAGE ONE resource for wireless networking!

Connect802 has the experience, expertise, and resources to help you with your wireless network system. Use your favorite search engine and see what Connect802 is doing. Each month we give you some suggested search terms for you to explore. Here's this month's list. As you look down the search engine results you'll find Connect802 either at the top, or on the first page (true for Google and Excite, unknown for the rest).

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