Bob and all,
The proper point is the 'halfway' point - half the power is -3 dB (10 log
0.5) but half the voltage is -6 dB (20 log 0.5).
The -3dB point would be used when plotting power curves, while the -6db
point is correct for voltage or current plots. Typical filters usually
assume a power curve (-3 dB) points unless stated otherwise. A plot of an
IF filter could be either depending on the measurement techniques. We are
moving closer to consistancy with the use of dBm in stating power gain (or
loss) within equipment like receivers, but I don't think everyone is on
board yet.
Yes, the advertizing folks sometimes take advantage of differences like this
to make their product look better - called 'specsmanship' in some
engineering circles. You have to read the really fine print.
73,
Don W3FPR
----- Original Message -----
Not sure where the -3dB comes from, maybe advertising? :-) Makes
the filter bandwidths look better.
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
