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A DC block is usually nothing
more than a capacitor that has low series reactance at the RF frequency,
and allows you to separate DC voltages along a transmission line.
A parallel coupled line can also serve as a DC block.
DC blocks can be placed in the
"hot" conductor of a transmission line such as coax, or
the ground plane, or both, as shown below. Many vendors offer coaxial
DC blocks in all three arrangements. When would you want a DC block
in the ground plane? Perhaps you want to inject a voltage onto the
source of a shunt FET, which is grounded to your fixture. Users
of this type of DC block must be aware that their equipment could
provide a voltage when they touch it. Careful where you drop that
of DC blocks