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Found: RF and Microwave Filters May be the Culprit in Cross Talk and Dropped Calls

(PRWEB) June 6, 2007 -- The devil is in the details. For system engineers who work for U.S.-based manufacturers of RF and microwave products, that seems to be the message. As products get rushed into the marketplace and put to the test by wireless service providers and consumers, shortcomings in frequency management come home to roost in the form of noise, cross-talk, signal dropouts and even complete transmission interruption. While the product design holds up under scrutiny on paper, test engineers are increasingly rooting out the source of the problem, and oftentimes the solution turns out to be one single component: the RF or microwave filter.



Of course, the difficulty in transmitting and receiving a clear signal stems, in large part, from competition for band space. Wireless service providers are quickly filling every available frequency gap from UHF frequencies of 300 Mhz, all the way up to super high frequencies of 30 GHz and beyond. Even the FCC can't bend the laws of physics, as useful bands quickly fill to capacity, forcing manufacturers to develop devices that operate within tighter bandwidths.

Cellular phone service providers, for example, despite utilizing competing multiplexing protocols, still run into conflict when signal frequencies are adjacent. For instance, the CDMA passband ends at 888.9 MHz, quickly followed by the GSM 900 passband, which begins at 890.1 MHz. With only 1.2 MHz of space, there is little room for error. Harmonics and other spurious signals add to the challenge of maintaining distinct borders between the two.

The only sentinels in guarding against interference across such relatively narrow gaps are RF and microwave filters. In general, the consequences of inadequate filtering translate into cross-talk and dropped calls for the cellular phone consumer; and loss of data and interrupted network connections for wireless LAN and WAN users. For the service provider, loss of customers represents the ultimate price to pay for failing to focus on filtering.

According to Sam Benzacar of Anatech Electronics, a New Jersey-based manufacturer that specializes in RF and microwave filter design, it's critical not to make the filter an afterthought. A defective product deployed in the field often requires sending out field technicians to swap out parts at base stations, for example. These costs frequently exceed any up-front expense to upgrade filter performance in the first place.

"Instead, at the start of design, look at the frequencies around the target band and ask what conflicting signals could appear in your specified time frame," advises Benzacar.

Benzacar points out that an engineer can insist on a filter with sharp cut-off and isolation. "A RF filter screening out a signal just 3 MHz away must be able to reject over 40 dB of signal strength outside its passband," explains Benzacar.

Even so, even the best of designs are occasionally compromised by an unforeseen frequency conflict. In such instances, it pays to work with a local component manufacturer who can readily modify its filters.

"A manufacturer may have to change the center frequency of a RF filter to improve the performance of its device within a particular band," says Benzacar. "A cost effective approach without scrapping the design is to initially work with a RF or microwave filter manufacturer who can quickly adapt a standard offering."

Sam Benzacar
Anatech Electronics, Inc.
Phone 973-772-4242
Fax 973-772-4646
www.anatechelectronics.com

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