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What Loran Signals Look Like
I was wondering what Loran signals look like. I took a few shots with the Tek 494P spectrum analyzer using my low band antenna (a 20m piece of wire slopping from about 50 feet down to 30 feet).
I am not very far from a powerful Loran station, Malone, FL LORAN, about 30 miles due south of Dothan, AL.
They run 800kW into a 700 foot monopole array. For more info see www.uscg.mil/d8/lorstamalone/default.asp
The signals are loud, in spite of the fact that my antenna is way too short and too low to be effective at that frequency. A tuned loop would probably work much better.
The first 3 pictures were taken with the analyzer in Peak-Hold mode for about one minute. The Loran signal being pulsed, a single sweep does not reveal the actual spectrum.
Screen shots courtesy of John Miles' 7470 emulator software with a Prologix GPIB-USB controller plugged in the spectrum analyzer.
This is a narrow Resolution Bandwidth (1 kHz) measurement. The RBW is too narrow to properly show the occupied spectrum.
This is a shot at wider RBW (10 kHz)
This is a shot with a 10kHz/div span and 10 kHz RBW.
This picture is in the time domain, using the spectrum analyzer as an oscilloscope (5mS/div)
You can clearly see the pulses, the different amplitudes come from different stations.
This picture is in the time domain also with a faster sweep (2mS/div)
Poul-Henning Kamp has interesting real time waveform plots (thanks phk!). His web site is choke-full of Loran information and lots of interesting projects!
http://phk.freebsd.dk/AducLoran/animation2.gif
http://phk.freebsd.dk/AducLoran/animation.gif
Links:
- John Miles' GPIB Toolkit, www.ke5fx.com
- Prologix, prologix.googlepages.com