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DC blocks are used in coaxial antenna systems to filter out audio and DC frequency interference. They use a capacitor to block low-level DC currents and allow higher frequency AC currents to pass through. They come in three forms and can be placed internally or externally in the system. However, external and internal/external DC blocks have a risk of electric shock due to their placement in series with the ground plane electrical wiring.
A direct current (DC) block is a frequency filtering device used in coaxial antenna systems. DC blocker allows radio frequency (RF) signals to pass while blocking audio and DC frequency interference that can damage your system. DC blocks are used in three different forms known as internal, external or internal/external. These components are further classified by connector type, voltage, and maximum frequency.
DC blocking works by using a blocking capacitor to capture the flow of low-level DC currents through a coaxial cable. It does this by allowing the higher frequency AC currents used in radio signal transmission to go through a process called coupling. DC blocking can produce restrictions on the transmission of all lower level frequencies, including AC frequencies, so system modification is sometimes necessary. This modification process is called circuit tuning.
These devices use a capacitor to filter out unwanted frequencies that could damage sensitive electrical components in laboratory test equipment or radio transmitters and receivers. Larger capacitors offer a lower cutoff frequency while smaller capacitors cut the transmission in a higher range. Where the various DC blocks differ is their placement in the coaxial system.
An internal DC block is connected in-line as an integral part of the main conductor of the coaxial system. Connected along the conductor, also called the system hot wire, this configuration is sometimes incorporated into specialized equipment to avoid the need for aftermarket parts and coaxial system modifications. When an external DC block is used, it is connected to the ground plane of the circuit, in series with the outer conductor of the coaxial cable. Combinations of the two systems are known as internal/external DC blocks. These blocking capacitors are incorporated along the ground plane and hot wire of the coaxial system.
The external and internal/external varieties of the DC block have a special feature that limits their use. Due to the fact that these devices are placed in series with the ground plane electrical wiring, they have the potential to carry current. This means that the configuration allows the operator of the equipment to receive a shock should he touch a charged piece of the system. These systems are sometimes used when it is necessary to inject current into a system for transmission modulation. Although the configuration presents a risk of electric shock, the risk is considered negligible when weighed against the benefits to the transmitted signal.
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