You have connected your hand-held VHF transceiver to an outside gain antenna. You now hear a mixture of signals together with different modulation on your desired frequency. What is the nature of this interference?

Hand-held transceivers typically feature broad front-end filtering to allow for wide-band frequency reception. While convenient for scanning, this design makes them highly susceptible to strong out-of-band signals. When you connect a hand-held radio to a high-gain external antenna, you feed it far more RF energy than its standard small antenna would capture. These numerous strong signals overwhelm the receiver's front end, mixing together in the internal RF circuitry to produce a jumble of unwanted signals and modulations on your desired frequency. This specific phenomenon is known as receiver intermodulation. It differs from audio stage overload, as the mixing of different modulations occurs in the RF front end before the signal is ever demodulated into the audio circuits.