Direction finding at ultra high frequencies (UHF): improved accuracy

Studies using radiotracking often require location accuracy attainable only by precise triangulation from short distances or homing to visual contact, operations severely impeded by large bearing errors caused by multipath pr opagation in wooded habitats. We found that over a frequency range of 151 t o 1,205 MHz, bearing accuracy in wooded habitat improved with higher direct ivity receiving antennas but was independent of frequency. Standard deviati on of error was as much as 4.7 times greater for a 4-element, 151-MHz Yagi than for a 17-element, 907-MHz Yagi, antennas of a size equally practical f or hand-held use. For visual spotting of arboreal animals, the radio-determ ined field area to be visually searched favored the 907-MHz antenna by a fa ctor of 22. These improvements in accuracy may be realized by direction fin ding on harmonics (>600 MHz) radiated by conventional (<220-MHz) wildlife t ransmitters. Also, weak harmonics were received at distances >100 m with in expensive, commercially available receivers that cover the frequencies of c onventional wildlife transmitters and their harmonics to over 1,000 MHz.