Which type of coupling is best for low frequencies?

The type of coupling that is best for low frequencies is direct coupling. Direct coupling allows for the transmission of signals without any additional components that could introduce losses or distortions. This means that signals, especially low-frequency ones, can pass through without being impeded by devices that could block or filter out those frequencies.

Direct coupling is beneficial because it maintains the integrity of the signal across different stages of amplification or processing. For low-frequency signals, this coupling method ensures that the full amplitude and waveform of the signal are preserved, allowing for accurate transmission and minimal signal degradation.

In contrast, other coupling methods may introduce capacitive or inductive reactance that can affect low-frequency signal transmission. For example, transformer coupling is often more suited for isolating stages and for AC signals, while impedance coupling can hinder low-frequency performance due to its reliance on matching impedances that can vary with frequency. Resistive-capacitive coupling, on the other hand, may filter out low-frequency signals due to the capacitive nature of the components involved.

Thus, the effectiveness and efficiency of direct coupling for low frequencies make it the best choice in this scenario.