HEH ADA272018.PDF refers. It may be transcribed as AD-A272 018
Technical Report 1617 Sept 1993 VLF Harold E Holt RADHAZ Measurements by PM Hansen and J Chavez
Or simply phone Raytheon at Harold E Holt, they are very helpful.
Or I can send a pdf.
There really is no difficulty or secrecy come to that, seek and ye shall find, ask and it will be given unto you.