A superheterodyne receiver is designed to receive signals with carrier frequencies between 4 and 6 MHz with transmitted bandwidths of 100 kHz each. It’s IF frequency is 850 kHz. What range of local oscillator frequencies is required using high-side injection ?

Explanation:

A superheterodyne receiver is designed to receive signals with carrier frequencies between 4 and 6 MHz with transmitted bandwidths of 100 kHz each. Its IF frequency is 850 kHz. The task is to find the range of local oscillator frequencies required using high-side injection.

Superheterodyne Receiver: A superheterodyne receiver is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. This is achieved using a local oscillator (LO) and a mixer.

High-Side Injection: High-side injection means that the local oscillator frequency (f_LO) is higher than the received signal frequency (f_RF). In this mode, the local oscillator frequency is given by:

f_LO = f_RF + f_IF

Where f_RF is the radio frequency and f_IF is the intermediate frequency. In this case, f_IF is 850 kHz.

We need to calculate the range of f_LO for the given range of f_RF (4 MHz to 6 MHz).

Calculations:

1. For the lower end of the RF range:

f_LO (lower) = 4 MHz + 850 kHz = 4.85 MHz

2. For the upper end of the RF range:

f_LO (upper) = 6 MHz + 850 kHz = 6.85 MHz

Therefore, the range of local oscillator frequencies required using high-side injection is:

4.85 MHz ≤ f_LO ≤ 6.85 MHz

Correct Option Analysis:

The correct option is: Option 3: 4.85 MHz ≤ f_LO ≤ 6.85 MHz

This option correctly identifies the range of local oscillator frequencies required for the given superheterodyne receiver with high-side injection.