VHF/UHF bands generally have favourable propagation characteristics in terms of penetration and coverage and so is being considered for cognitive radio (CR) communications. Delay spread is an important parameter that needs to be considered in the design of a communication system. Using Root mean square Delay Spread (RDS) models, we can design a cognitive radio in such a way that it is adaptive to the RDS of the fading channel, thus minimizing errors in transmission of signals. Therefore, we propose a novel RDS model which incorporates the effects of propagation distance, transmitter height and transmitter carrier frequency. Finally, measured delay spread was compared with the proposed model and known delay spread models favourably. © 2018 Electromagnetics Academy. All rights reserved.