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Today, a friend who uses a Mackox oscilloscope asked me what it meant by the channel isolation value listed in the oscilloscope’s specifications, which is indicated as 40 decibels or more. So let’s discuss what the isolation parameter between oscilloscope channels means and how to measure the channel isolation of your own oscilloscope. We know that most oscilloscopes available on the market today do not have isolation between channels; in other words, they share a common ground. Therefore, crosstalk is inevitable between channels. Crosstalk is a measure of the extent to which the signal on one channel affects another channel. Ideally, channels should not interfere with each other, but this is not the case in reality. Coupling, mutual inductance, and mutual capacitance between two signal lines can cause noise on those lines, making crosstalk inevitable. The isolation between channels indicates the level of interference between them; a higher value means stronger resistance to interference. So, how exactly is it measured? We apply a sine wave signal to channel 1 of the oscilloscope as an interference channel, and adjust the vertical scaling of channel 1 so that the waveform fills the entire oscilloscope screen as much as possible. Then adjust the vertical level of Channel 2 to the minimum, set the channel attenuation ratio to 1X, use Channel 2 as the interfered channel, and ensure that no signal is fed into Channel 2. Adjust the time base setting of the oscilloscope so that the signal from channel 1 displays at least one complete cycle on the screen. Open the measurement options of the oscilloscope to obtain the amplitudes of Channel 1 and Channel 2. At this time, the vertical scale of Channel 1 is 500 mV/div, and the amplitude is 3510 mV. The vertical scale of Channel 2 is 1 mV/div, and the amplitude is 0.74 mV. The formula for calculating channel isolation is: where K1 represents the vertical level of Channel 1, K2 represents the vertical level of Channel 2, A1 represents the amplitude of the signal in Channel 1, and A2 represents the amplitude of the signal in Channel 2. The calculation of the logarithmic value yields approximately 6.38; therefore, the channel isolation of the oscilloscope at this point is 127.6 dB, which meets the requirement of ≥40 dB specified in the parameter table. The greater the channel isolation of an oscilloscope, the less crosstalk between channels there is, and thus the more accurate the tests become. Friends who are interested can pick up their oscilloscopes and conduct simple tests and calculations.