HP HP-Bench-Briefs-1973-04 free download

File name HP-Bench-Briefs-1973-04.pdf

VOLUME 13 NUMBER 1 APRIL 1973 2 What's a power Pout exceeds the reference power Pref is defined by dB and dBm? N (in dB) = 10 log k 1 Pref 0 N i s negative when Pwt is less than %' j That's a question often asked in the p, -? service shop, especially when work- ing with high frequency signal The non-linearity of logarithms can -2 Sources or measurement gear, such be Seen by plotting it On linear graph -3 as a spectrum analyzer. paper. Assume we are measuring the output power of a variable gain The decibel (dB) i s an arbitrarily de- amplifier. The input power (pref) fined unit of transmission gain (or is held constant at watt. loss) that has come into general use From the graph of log values (Figur since about 1925.Developed for use s I , we determine that the log of 2 ) in the telephone industry, it was is 0.3, and therefore the gain of the named the bel, in honor of the in- above circuit i s 3 dB. Note that the ventor of the telephone, Alexander plot i s a straight line (linear) because Graham Bell. one scale of the graph is logarithmic. Assume now that the output power is 0.5 watts for the same 1 watt input power. What i s the gain in dB? Note that when Pout equals Pref(that i was found to be very con- Several very useful conversions for comparing two power can be made: r, N, of dB by which the Y O U R PRIVATE LINE TO H P C U S T O M E R SERVIC * I -2