Final answer:
The use of two frequencies in secondary radar transactions allows for the differentiation between the transmitted signal and the echo, which eliminates signal ambiguity and increases measurement accuracy through the Doppler effect.
Step-by-step explanation:
The use of two frequencies in secondary radar transactions eliminates issues related to the ambiguity of received signals. By comparing the frequency of the transmitted signal with the frequency of the echo, the system is able to produce beats. These beats are the result of mixing the double Doppler-shifted echo with the original frequency. In cases like police radar, which operates at frequencies such as 1.50×10⁹ Hz, this technique helps determine the speed of moving vehicles through the Doppler effect. The received echo experiences a frequency shift that corresponds to the relative velocity of the moving object, such as a car.
Secondary radar transactions are improved through the use of multiple frequencies as it allows for more accurate determination of the position and speed of objects and helps in avoiding signal interference, which is a risk when devices operate within the same frequency ranges used by essential communication and medical equipment.