Output+Power+Protection

__**Output Power Protection**__

Theoretically, the results of both the simulation and the actual board tests show that the system has a possible gain of 57 dB. This is the gain necessary to increase the minimum discernable signal to a level that can be read by the ADC. However, one must also consider the maximum discernable signal level. If the dynamic range of the system is 75 dB, then the maximum discernable signal is -32 dBm. When 57 dB of gain is added to that, the result is a maximum input signal to the digital side of the system of 25 dBm. This is an input power of around 40 mW, and an input current of around 80 mA. The AD9460 does not expect an input current much beyond 35 mA. Therefore, a series PTC was placed at the output of the RF front end circuitry. This way, if the RF board ever tried to push more than 35 mA of current, the circuit will blow, but will be useable again after a power reset. For increased range, an attenuator was placed at the output of the circuit (7 dB). However, to detect the smallest signals possible, the attenuator should be removed. The circuit can still detect the minimum discernable signal without the attenuator. However, the system is more accurate with extremely low-level signals with the attenuator off.