Detector Log Amplifiers
A Detector Log Amplifier is the receiver section of a radar system which was adapted from the old concept of Morse Code for telegraph pulse communications in the late 19th century.
Basically, a radar system uses a pulse amplitude modulation concept where a microwave switch toggles a microwave signal off and on at the emitter site using any type of digital data signal. The receiver (or DLA) picks up the signal, and the result is pulsed output with the same digital code the emitter has picked up. The only difference is that the pulsed output amplitude of the DLA depends on the input signal strength.
Therefore, the function of the DLA is not only receiving pulse amplitude decoding, but determining the signal strength as well. Also, due to the logarithmic nature of this part, the DLA covers a wide dynamic range. Often, an analog-to-digital converter is used after the DLA to determine the input signal level, as well as for digital decoding.
The following article is a basic theoretical analysis of a Detector Log Amplifier, a single detector approach to the DLA. A more complex DLA, called ERDLA, employs two or more detectors and is based on the same concept.