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“ ionospheric propagation since Godfrey said that “the Over-
WSPR technology 1956, when a definitive set The-Horizon-Radar (OTHR)
capability has been con-
of experiments showed that
is not new and has the ionosphere is generally tinuously improved since
sufficiently stable for a HF
1956. OTHR uses multi-hop
been used by the US ionospheric radar to succeed (or multi-skip) ionospheric
military since 1956. in over-the-horizon aircraft propagation in the HF fre-
detection.
quency range of 3 MHz to 30
As a result, the paper said, MHz, just like WSPR. OTHR
US military has developed is capable of accurately
In November Godfrey, several Over-The-Horizon- detecting aircraft over large
Coetzee and Maskell followed Radar (OTHR) systems over distances and propagations of
up their location report with the years, that have been in up to round the world (RTW)
a paper that documents the operation since 1961. have been observed.”
extensive use of the technol-
ogy WSPR is based on which These OTHR systems have “A number of experiments
has been in use since the been deployed in Chesapeake have been conducted by the
1950s. Bay, California, Virginia, US Air Force, Air Development
Maine, Aleutian Islands,
Center in Rome, Georgia to
WSPR uses High Frequency England and Australia. test the RTW propagation
(HF) ionospheric propagation distances and the accuracy
to send signals around the According to the paper, the of detecting and targeting
world. Typical frequencies are US military tested Round- aircraft.
in the range 3 MHz to 28 MHz. The-World propagation
Transmission power levels are successfully in 1978 and More than 120 books have
up to 5 W continuous and the tested Precision Targeting of been written about the bizarre
duration of the transmission is Aircraft successfully in 1985. disappearance.
110.6 seconds. Typical frequencies are in Hopefully as the tenth
the range 3 MHz to 30 MHz.
The US military (Air Force Transmission power levels are anniversary of the tragic disap-
and Navy) has invested up to 25 kW with a pulse width pearance nears a search will
heavily in research into HF of 100 µs. be formerly announced.•
The actual aircraft that was lost
photographed in Perth. ©Alan Pepper
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