Question

If the incoming signal to the mixer is 3,600 kHz and the first IF is 9 MHz, at which one of the following frequencies would the local oscillator (LO) operate?

a) 5,400 kHz
b) 9 MHz
c) 12,600 kHz
d) 15,600 kHz

Answer 1

The local oscillator (LO) would operate at a frequency of 12,600 kHz, which is the sum of the incoming signal frequency (3,600 kHz) and the first Intermediate Frequency (IF) of 9 MHz (or 9,000 kHz).

Step-by-step explanation:

If the incoming signal to the mixer is 3,600 kHz and the first Intermediate Frequency (IF) is 9 MHz, to determine the operating frequency of the local oscillator (LO), you need to apply the principle that the LO frequency is the sum of the signal frequency and the IF when the mixer is up-converting (which is the common scenario in superheterodyne receivers). Therefore, the LO frequency must be the signal frequency plus the IF frequency.

In this case:

• Incoming signal frequency = 3,600 kHz
• First Intermediate Frequency (IF) = 9 MHz

The LO frequency would be:

3,600 kHz + 9,000 kHz (since 9 MHz = 9,000 kHz)

LO frequency = 12,600 kHz

So, the correct answer is c) 12,600 kHz.