|Magnetic field lines in the |
magnetosphere (Ill. NASA)
The round-trip time varies with the latitude of the transmitter, or to be more accurate with the position relative to the magnetic Equator. Typical delay times are 140 - 300 ms. At my location near Oslo, Norway, the expected delay is about 308 ms, but unfortunately I have yet to hear such an echo.
210-220 ms delay time
It has a delay of 210-220 ms, consistent with his location in Northern England. The transmitted signal was a chirp using a 100 Watt SSB transmitter with a 50 m longwire antenna. Note the stereo effect as the transmitter and receiver are in the right and left channels respectively. The chirps are exactly 5 sec apart, timed against GPS, so this will enable one to calculate the exact samplerate, which is about 8100Hz. Listen to the signal here (with kind permission from P. Martinez, G3PLX).
- P. Martinez (G3PLX), Long Delayed Echoes, A Study of Magnetospheric Duct Echoes 1997-2007, Radcom, Oct 2007, pp. 60-63.
165-168 ms delay time
I would like to offer an alternative explanation as it is very seldom that signals at this low frequency travel around the world. At his location in Georgia, US, the magnetospherically ducted delay was 143 ms at the time, only 5 ms more than the round-the-world travel time, so his observed delay can just as well have been a magnetospherically ducted echo. See the picture to the right which shows the path it could have taken, which in this case only goes out to about 1 earth radius. Listen to the signal here (with kind permission from G. Greneker, K4MOG).
- G. Greneker (K4MOG), “The Ultimate DX: An Around the Earth Path,” QST, June 2007.
- S. Holm (LA3ZA), “Magnetospheric ducting as an explanation for delayed 3.5 MHz signals,” QST, March 2009.