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LOg amplifier AD 606


as a Radio Amateur I am doing some developmentin controlling output signalof radio equipment.I made a circuit by using AD´s log amp AD 606. Recently I checked the flatness of Vlog versa frequency between 2 to 30 MHz.Here I realized a variation of about 1.5 db. As shown in the amplifiers data sheet, one could get it flat by connecting a capacitor of 150 pF at pins 11 and 12. Trying this I had no   success. The Vlog did not alter at all at the corner frequency of about 3 mc. At the Input FIL pins I use capacitors with 150 pF closely tolerated. Grounding appears to be ok. Are these chips maybe defective or whatsoever? What can be done to get a flat response over a limited frequency band?

Thank you very much indeed.


Sen. Eng. of University of Munich