How to use the single arm bridge of 3dB bridge

　　A single arm bridge, where the measured resistance is one bridge arm and the standard resistance is one bridge arm. An ammeter is connected between the two bridge arms. When the measured resistance is the same as the standard resistance and the current is zero, the reading of the standard resistance is the measured resistance value.

　　By adjusting the values of R2, R3, and R4 through a bridge, when the bridge is balanced, R1=R2 × (R3/R4) can be used to measure the measured resistance. From the graph, it can be seen that the measured resistance of R1 includes lead resistance and contact surface resistance. Therefore, the actual resistance should be subtracted from the lead resistance and contact surface resistance. The smaller the measured resistance, the greater the lead error. Therefore, a single arm bridge is commonly used to measure resistance above 1 ohm, with a typical range of 1 to 99990 ohms. For switch contact resistance, which is generally in the micro ohm range, this bridge should not be used because the lead resistance is in the milliohm range and cannot be measured. In this case, a double arm bridge can be used. R1 is the measured resistance, R2, R3, R4 are adjustable resistors, P is the ammeter, E is the battery.

　　An ideal filter should have a completely flat passband, such as no gain or attenuation within the passband, and all frequencies outside the passband should be completely attenuated. In addition, the conversion outside the passband should be completed in a very small frequency range. In fact, there is no ideal bandpass filter. Filters cannot completely attenuate all frequencies outside the expected frequency range, especially when there is an attenuated but not isolated range outside the desired passband. This is commonly referred to as the roll off phenomenon of filters and is represented by the attenuation amplitude dB per decade. Usually, the design of filters should strive to ensure that the roll off range is as narrow as possible, so that the performance of the filter is closer to the design. However, as the roll off range becomes smaller, the passband becomes no longer flat - "ripples" begin to appear. This phenomenon is particularly evident at the edge of the passband, known as the Gibbs phenomenon.

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