*Question E4D11:
Why are odd-order intermodulation products, created within a receiver, of particular interest compared to other products?*  

*Correct Answer is  A: Odd-order products of two signals in the band being received are also likely to be within the band*  

### AI Response: (may contain errors)  

Odd-order intermodulation products are of particular interest in radio receivers because they can fall within the band of interest, potentially causing interference with the desired signals. Let's break down why the correct answer is correct and why the other choices are incorrect.

### Correct Answer:  
**A: Odd-order products of two signals in the band being received are also likely to be within the band**

- **Explanation**: Odd-order intermodulation products, such as the 3rd, 5th, and 7th order, are generated by non-linear mixing of signals. For example, if two signals at frequencies $f_1$ and $f_2$ are present, a 3rd-order product can be calculated as $2f_1 - f_2$ or $2f_2 - f_1$. These products are more likely to fall within the same frequency band as the original signals, causing interference.

### Incorrect Choices:

**B: Odd-order products are more likely to overload the IF filters**

- **Explanation**: Overloading of IF filters is generally related to the amplitude of signals rather than the order of intermodulation products. Both even and odd-order products can cause overload if they are strong enough, but this is not specific to odd-order products.

**C: Odd-order products are an indication of poor image rejection**

- **Explanation**: Image rejection is related to the ability of a receiver to suppress signals at the image frequency, which is a different issue from intermodulation. Intermodulation products are not directly related to image rejection performance.

**D: Odd-order intermodulation produces three products for every input signal within the band of interest**

- **Explanation**: While odd-order intermodulation can produce multiple products, the statement is misleading. The number of products depends on the specific order and the number of signals involved, not a fixed number like three for every input signal.

### Useful Formula:

For two signals at frequencies $f_1$ and $f_2$, the 3rd-order intermodulation products can be calculated as:
- $2f_1 - f_2$
- $2f_2 - f_1$

These products are of particular concern because they can easily fall within the band of interest, leading to interference with desired signals.