Fj is a function of frequency, varying from near unity (less than f5 dB) at frequencies below 10 MHz to about 0.1 (-20 dB) and 0.01 (-40 dB) at 100 MHz and 400 MHz, respectively. Since Fj is independent of distance there is no exponential attenuation of ultrashort-waves in the jungle. In fact the effect of the jungle on the direct wave must be almost identical to that on the reflected wave in order not to disturb the almost complete cancellation.