‰ NOW 15 WPM ‰ TEXT IS FROM JANUARY 2016 QST PAGE 48 ‰ THE DF LADDER, THERE ARE MORE EXPENSIVE, OFF THE SHELF DEVICES FOR ANALYZING THE SPECTRUM, RANGING FROM A FEW HUNDRED DOLLARS INTO THE THOUSANDS. THE LITTLE BOOK ALSO INCLUDES SOME INTERFERENCE MITIGATION TECHNIQUES, TO USE IN CASES WHERE YOU MAY NOT BE ABLE TO ELIMINATE THE PROBLEM AT ITS SOURCE, BY USING FERRITE DEVICES AND ELIMINATING COMMON MODE ISSUES IN YOUR SHACK. THERE ARE SOME GENERAL REFERENCE MATERIALS TOO, INCLUDING THE OHMS LAW WHEEL, FIELD STRENGTH, ANTENNA FORMULAS, DECIBEL ‰ END OF 15 WPM TEXT ‚