Last night, Edgar J. Twining in Moonah, Tasmania has successfully picked up several Loran-C signals from the other side of the world. He was using an E-field antenna connected to his Excalibur receiver, tuned to a 6 kHz band around 100 kHz. For phase and timing reference, the rising edge of 1pps pulses from a GPS device was capacitively injected to the antenna line. In the wee hours between 18 and 19:50 UT, Edgar produced a set of four 20-minute recordings, which were then postprocessed here using my homebrew "LoranView" averaging software.

 

Attached image is the result using one-minute averaging. Each of the 40 columns corresponds to the repetition rate and delay of a single Loran station, dual rated stations appear twice. The order of slots is generally west to east, with the exception of the GRI 7950 chain at the right which has been added later. Horizontal timescale within each slot is equivalent to the 12 kHz samplerate, ie. 83 us per pixel or 2 ms in each slot. Vertical scale is one pixel per minute, from 18 (bottom) to 19:50 UT (top), with three 11 minute interruptions due to the gaps between files. Colour hue corresponds to received carrier phase, referenced to the 1pps pulse shown in the leftmost slot. The slots for the Chinese navigation stations are empty as these have been off air for a couple of days, presumably for maintenance.

 

Edgar's is getting solid traces even from his furthest station, Lessay at 17521 km, which is radiating 250 kW peak or about 3 kW average power on each of the two rates. As all Loran stations share a common frequency band, the fact that he doesn't have nearby stations probably helps to reduce crossrate clutter, allowing him to fully exploit the sensitivity of his excellent receive setup.

 

Interestingly, the colour of the very distant traces is changing only slowly, indicating phase stability of the path on the order of an hour or so. This confirms that sub-milliHz bandwidths can indeed be useful to enhance slow weak-signal communication on 137 kHz.

 

Best 73,

Markus (DF6NM)

 

 

Von: Markus Vester <[email protected]>
An: edgarjtwining <[email protected]>
Verschickt: Do, 25 Sept 2014 11:34 pm
Betreff: Re: Loran - Europe!