( ( The ( received ( radio ( frequency ( carrier wave ) ) ) ) ) ( ( ( is ( mixed ( with ( ( a ( local signal ) ) ( of ( different frequency ) ) ) ) ) ) ( to ( generate ( a ( ( useful beat ) frequency ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ received) (NN radio) (NN frequency) (NN carrier) (NN wave)) (VP (VBZ is) (ADJP (JJ mixed) (PP (IN with) (NP (NP (DT a) (JJ local) (NN signal)) (PP (IN of) (NP (JJ different) (NN frequency)))))) (S (VP (TO to) (VP (VB generate) (NP (DT a) (ADJP (JJ useful) (JJ beat)) (NN frequency)))))) (. .)))
The received radio frequency carrier wave is mixed with a local signal of different frequency to generate a useful beat frequency.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS waves)) (PP (IN of) (NP (CD two) (JJ different) (NNS frequencies)))) (VP (VBP interfere)))) (, ,) (NP (NN beating)) (VP (VBZ occurs)) (. .)))