( ( ( ( Radio waves ) -- ) ( ( Electromagnetic waves ) ( of ( ( relatively low ) frequency ) ) ) ) . )
(ROOT (NP (NP (NNP Radio) (NNS waves)) (: --) (NP (NP (JJ Electromagnetic) (NNS waves)) (PP (IN of) (NP (ADJP (RB relatively) (JJ low)) (NN frequency)))) (. .)))
Radio waves --Electromagnetic waves of relatively low frequency.
(ROOT (S (NP (NNP Am) (NN radio) (NNS waves)) (VP (VBP exist) (PRT (RP in)) (NP (DT the) (ADJP (QP (CD 540) (TO to) (CD 1600))) (NN khz) (NN frequency) (NN range))) (. .)))