[Elecraft] Talking filter Bandwidths

[W3FPR - Don Wilhelm]

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.
>