Posted by
Ed Muns, W0YK on
Aug 19, 2008; 6:28pm
URL: http://elecraft.85.s1.nabble.com/How-do-you-measure-filter-offset-tp733034p733782.html
> You only need the two -6 dB points, which can be measured to
> a resolution of
> 1 Hz and 0.1 dB using the internal AFV/dBV function.
This is true if the filter passband is flat, but I've found both ripple and
slope in some INRAD filter passbands, so I always want to see the entire
sweep to make sure I'm finding the true bandwidth.
> You
> should set AGC Off and ensure WIDTH (i.e. the DSP BW) is >>
> than the filter you are measuring...otherwise you're
> measuring the combination of XFIL plus DSP. I do this by
> disabling all filters except the one under test and setting WIDTH
> >> XFIL BW. Once you have the two -6 dB points, then you can
> figure how
> much offset to enter so these two points are equidistant
> about the center.
Yes. Thanks. These are important points to get valid measurements. Also
make sure you are within the passband of the K3 audio circuitry. For
example, it rolls off below 300 Hz. And, of course, that the RX equalizer
needs to be flat.
73,
Ed - W0YK
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