Propagation planning, by a mixture of observation and computer simulation, is necessary if the system is to work properly. At UHF and VHF frequencies, the effects of obstructions is significant. This significantly increases in urban environments. Studies have indicated that a relationship is more often followed than a law. Effect of street orientation.
Streets have a significant waveguide effect.
Variations of up to 20dB have been measured in urban environments as a result of street direction. Effects of foliage. Propagation in rural areas is significantly effected by the presence of leaves. Variations of 18dB between summer and winter have been observed in forested areas. Effect of tunnels.