Notes on IF Rejection
This test measures a receiver's ability to reject signals that have the same frequency as the receiver's first IF.

The test is simple, using one signal generator connected to the receiver's antenna port and a true RMS AC voltmeter connected to the receiver's AF output. The signal generator is set at the IF frequency, and then the power is cranked up until the AC voltmeter shows in 3 dB increase in the noise.

Theoretically, it should be easy to filter signals at the IF frequency, because they are far removed from the frequency of interest. However, these days the filtering in receiver front ends is frequently rudimentary, and there are plenty of powerful shortwave stations that could be problematic. Problems with IF rejection are disastrous, because the interfering signal will be heard no matter where the receiver is tuned.