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

Intermodulation products are created when signals mix inside a receiver. Odd-order products, particularly third-order products (calculated as 2F1 - F2 or 2F2 - F1), are highly problematic because their resulting frequencies fall very close to the original frequencies. If two strong signals are present within the same amateur band, their odd-order intermodulation products will likely also fall within that same band. This means the receiver's standard front-end band-pass filters cannot block them, and they will appear as spurious signals interfering with desired weak signals. Even-order products (like F1 + F2) generally fall far away from the original band and are easily rejected by the receiver's front-end filtering. Therefore, odd-order products are the primary concern for in-band interference.