Скачать или смотреть 420Mhz multipath fading between two fixed radio sites

This receiver is monitoring a Control Channel (cc) on a nearby 400Mhz P25 trunking radio site. Both the transmit (Base) site and the receive antenna were completely stationary for the duration of this video. In this case, the path distance between the two sites is only 4 miles, however, there is a tree covered hill obstructing the Line of Sight path. The deep signal fading being observed here is common on UHF frequencies and is caused in this case by multipath signals cancelling out (or adding) to the received signal strength. This effect is also known as Rayleigh or Ricean fading. The important aspect of this demonstration is the degree and depth of fading that can often be experienced on UHF frequencies, even over relatively short distances, if there is any obstruction within the freznel zone along the signal path. This foliage induced fading would be much less severe on VHF frequencies. This should raise alarm bells for fire agencies who are increasingly being compelled to migrate away from proven analogue VHF radio networks, to UHF digital networks. Similar effects occur in metropolitan areas where signals bounce off buildings and arrive at the receiving station at different phases. In cities though, generally the buildings do not sway around in the breeze and it is the motion of the mobile/portable station that causes the Rayleigh effect and P25 signals to breakup and go garbled, even in strong signal areas..