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External Cross-Modulation

February 18th Fact-of-the-Day

External cross-modulation refers to conditions where two or more radio frequency signals cross-modulate outside transmitting or receiving equipment and generate spurious frequencies. Common causes include nonlinear (rectifying) connections in ground circuits, between sections of electrical conduit, between spliced antenna guy wires, between sections of metal towers, between component parts of nearby antennas, or between sections of nearby power or telephone lines. Where external cross-modulation occurs in circuits conducting AC or telephone audio currents, AC hum or telephone audio usually modulates the spurious radio frequencies, providing a clue as to the source of the problem. External cross-modulation is especially troublesome where two or more transmitters share facilities, such as at mountain-top repeater sites or where tall communication towers are shared by multiple users. ©2005 Martek International All rights reserved.


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