RE: How do you measure filter offset

Posted by Bill W4ZV on Aug 19, 2008; 6:18pm
URL: http://elecraft.85.s1.nabble.com/How-do-you-measure-filter-offset-tp733034p733740.html

Ed Muns, W0YK wrote

Another method, more laborious, but fairly accurate is to use the Elecraft
XG1 or XG2 to inject a stable signal at the antenna port and deploy the dbV
function in the K3 to measure the amplitude every 10 Hz or so.  Plot the
data manually or by entering into a spreadsheet that produces a graphic of
the IF response.

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.  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.

73,  Bill