Description
DC blocks are coaxial components that prevent the flow of direct current (DC) signals into systems while allowing higher frequency RF signals to pass through. DC Blocks are installed in a system to stop any signal with a frequency of Zero Hz (DC) from interfering with sensitive RF components. The DC block works as a high-pass filter, allowing only RF frequencies to pass through. They are typically designed by placing capacitors in series with a transmission line.
DC Blocks are used in applications such as ground loop elimination, signal source modulation leakage suppression, system signal-to-noise ratio improvement, test setup isolation and other situations involving unwanted DC signals. They are broadly utilized in defense, commercial wireless, quantum computing, and test and measurement applications.
Three types of DC Blocks
Inner DC blocks: Inner DC Blocks have capacitors placed in series with their center conductors. They prevent the flow of DC and minimize the flow of low-frequency currents while providing minimum impedance to RF signals.
Outer DC blocks: Outer DC Blocks have capacitors placed in series with their outer conductors. They prevent the flow of DC and low-frequency current surges along the outer conductors of transmission lines.
Inner/outer DC blocks: Inner/outer DC Blocks have capacitors placed in series with both their outer and inner conductors. This prevents DC from passing along both conductors, typically in a coaxial connection.
Main parameters of DC Blocks
Frequency: DC blocks are typically optimized for a frequency range, meaning that they block all DC signals and allow RF signals in a specific frequency range.
Voltage rating: also known as breakdown voltage or maximum voltage, is the maximum voltage that a DC block can take before it breaks down. The higher the voltage the better the rating.
Insertion loss: is the amount of the loss of RF Signal that passes through the DC Block. Ideally this would be zero.
Impedance: DC Blocks should be matched to the characteristic impedance of the system in which they are implemented. Majority of RF systems are 50-ohm, but also 75-ohm DC blocks are available.
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