E6E04 (D)
What technique is used to construct low-cost, high-performance crystal ladder filters?
A. Obtain a small quantity of custom-made crystals
B. Choose a crystal with the desired bandwidth and operating frequency to match a desired center frequency
C. Measure crystal bandwidth to ensure at least 20% coupling
D. Measure crystal frequencies and carefully select units with a frequency variation of less than 10% of the desired filter bandwidth
