Hello All. I just stumbled upon this announce (I'm not the seller and I'm not related to him in any way) for a Tracor 599k VLF/LF tracking receiver with manual included. It has a chart plotter for phase difference. http://www.kijiji.it/annunci/altro-elettronica/pistoia-annunci-buggiano/tracor-599k-vlf-lf-receiver/80388385 Andrea