Averaging by convention means an arithmetic average and that by definition means taking all the elements of a set, adding their values together and dividing by the number of elements. That works fine in linear space. If you try that in log space, you get a geometric rather than an arithmetic mean. Adding logs is the same as multiplying, and dividing logs is taking a root, and a geometric mean is the nth root of the product of the n members in a set. Here is a simple example. Let's say there's a broadband signal and the first sweep you get 40 dBuV, and the second time it is 0 dBuV (noise floor). If you perform video averaging in log mode you get a 20 dBuV answer. If you go to linear mode, you get : 0.5* (100 uV + 1 uV) = 50.5 uV = 34 dBuV, a 14 dB difference.
on 12/12/01 10:31 PM, KC CHAN [PDD] at [email protected] wrote: > > Hi all > > Someone told me that when doing the video averaging(set it small, say 10Hz), > you need to use linear scale(uV) instead of log scale(dBuV). What is the > reason behind about this? > > Best Regards > KC Chan > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old messages > are imported into the new server. > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
