🔍 Key Concepts

• Mixer circuits in marine radar – how the received echo signal and local oscillator signal combine in a nonlinear device (diode) • Intermediate frequency (IF) – the difference between the transmitted/local oscillator frequency and the received echo frequency • What happens in a mixer diode when one of the inputs (echo) is missing

💭 Think About

• Think about what a mixer actually produces from its inputs – sum and difference frequencies of the signals fed into it. What signals are present when there is no echo? • Is there still any RF or local oscillator signal at the mixer, even when no targets are present on the scope? How does that affect the output? • Consider whether the crystal diode can generate an output IF frequency with only one signal applied instead of two.

✅ Before You Answer

• Identify which frequency in the choices looks like a difference (IF) frequency between the radar operating frequency and the local oscillator frequency typically used in X‑band radar problems like this. • Decide whether a continuous-wave (CW) output can exist at the IF if only the local oscillator is present at the mixer input. • Confirm whether a nonlinear device like a diode mixer can produce the stated outputs without a second input signal (the echo).