Cybthia , here are some recommendations : AT&T and most of the Tel Companies would like to see a 6 db margin. The 3db margin is acceptable to most test houses. Zero dB margin follows the letter of the law.Taking componet tolerances into consideration you might "skate on thin ice" !. In most cases using high quality test equipment +/- 2 % tolerances in test equipment should be acceptable.
Frank.
