A two – tone test method, determines the presence of inter-modulation distortion. Two sinusoidal frequencies of equal amplitude are introduced are introduced into the system under test. The two frequencies are spaced close together with reference to the unit under test (an amplifier, receiver, transmitter) is monitored on a spectrum analyzer that is comparable in characteristics to suspect system. The resultant display should be an exact reproduction of the input frequencies. If not, some form of inter-modulation distortion is present. To determine the if external; sources are causing the inter-modulation distortion; you can use a single frequency signal. If the display on the spectrum analyzer does not show the single frequency, the inter-modulation distortion present.

Inter-modulation distortion cannot be entirely suppressed, but it can be minimized by scheduling components and circuitry, parasitic suppression circuitry and antenna spacing. These factors are incorporated in the design of the system and are tested during production. Any shields or parasitic suppressors that are removed by the technician must be replaced before troubleshooting and/or repair can be effective. Antenna locations also pose a consideration when installing a new system. Ship alteration specifications must be observed when new antenna systems are being installed.