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Double-pole double-throw (DPDT) relays have long been used as the switching mechanism for applications such as attenuators, circuit and component bypassing and other specialized circuits such as selecting between unity and a preset amplifier gain. These applications are all loosely described as bypass circuits. To create the bypass, circuit designers traditionally have externally joined either the normally open (NO) or normally closed (NC) positions of a DPDT relay on the circuit board. However, when applied to higher frequencies and decreasing signal strength, this technique causes unwanted additional signal attenuation or fidelity loss due to the additional circuit connections, added circuit lengths and circuit materials.
Given a sufficiently small signal, these factors may cause signal attenuation to the point of rendering the signal useless. An example of this condition is in cellular communications where the transmit signal generated by the base station may be many watts in strength. The remote hand-held unit has no trouble receiving this signal, yet it must transmit back through the antenna to the base station. The remote unit's transmit signal is weak comparatively, requiring the base station to amplify the signal directly at the receiving antenna to counteract further signal loss through lengths of cabling to the final amplifiers. Mounting an amplifier directly at the receive antenna...