1. How is BEF used in base station applications?

Mike Johnston (muRata): As far as muRata is concerned, we have never offered any individual Band Elimination Filters for celluar base stations. The vast majority of our BEF product is found in lower-frequency piezoelectric filters (BAW types) used in commercial TV receivers in the 4-6MHz range. However, we do have, and will continue to offer especially in the Dielectric Resonator (our so-called "Gigafil") style, duplexers which may employ a combination of band-pass and band-stop filters in a single package.

2. How do I choose between a ferrite filter or an LC-based filter?

Dave Arthurs (Spectrum Control): A ferrite chip is specified by impedance and based on its impedance at a given frequency will yield a certain amount of attenuation in a circuit. Typically this attenuation will be less than 15 db and will very somewhat with the change of impedance versus frequency. An LC filter will employ the impedance of a ferrite or the inductance of a wound inductor (depending on the filter type) along with a feed through capacitor. Depending on the values of each it will have a certain cut-off frequency. Above the cut-off frequency the insertion loss of the filter will increase by 40db/decade – considerably more that the ferrite chips. Choosing between the two types of filters is by matching the required attenuation to rated insertion loss of the filter.

3. Does anyone have multifrequency bandpass filters? — For example, a filter that would pass 133MHz and 267MHz.

Mike Johnston (muRata): muRata offers a certain number of application-specific "combo" SAW filters, especially for the popular GSM cellphone bands, and others. To see our complete selection, use the search function at our Web site, with the prefix SAWE* to initiate a wild card search for all dual-band SAW filters.

4. Do you offer L1/L2 dual band SAW filter?

Mike Johnston (muRata): This issue is not so much one of technology, but of market. muRata typically does not serve military markets, and therefore has not developed a SAW filter for the so-called "L2" GPS band (1227 MHz), which is utilized as a high-resolution positioning service not available to commercial GPS user at "L1" (1575 MHz). However, even with the "degraded" resolution (poorer than +/- 10 meters) offered at 1575 MHz, there are differential GPS techniques which can achieve accuracies down to a few millimeters in surveying and geological applications.

5. What is the maximum temperature range for the thin film and the thick films?

Larry Eisenberger (AVX): Both thick film and thin film capacitors are rated to work from -55 °C to +125 °C.