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Bias Tees allow DC currents and/or voltages to flow to RF devices while blocking RF and microwave signals on the same line. DC blocks are high pass filters with cutoff frequencies down to audio frequencies and DC. Bias tees are used in a range of applications, including mobile phone amplifiers and test and measurement devices. They can be used together at a node where DC power or bias voltage/current is needed, but they would be disruptive if they were used further down the RF transmission line.