[Elecraft] How do you measure filter offset [K3]

[Ed Muns]

> I don't understand what the filter offset is really doing. My 
> 2.7 KHz filter for example is -0.87. I assume this means 870 
> Hz offset from something. What reference is the offset from? 
> Does this mean that the IF frequency is actually shifted from 
> some nominal value?

If the filter is not centered on the IF, then the resultant offset can be
entered into the filter configuration in the CONFIG menu so the firmware can
make the correction so that the filter is centered on the IF.

> Could someone explain a method of measuring roofing filter 
> offset? I have spectrum analysis software. Soon [I hope] I 
> will have the second receiver and I will possibly be setting 
> up a compromise offset for two filters. I paid a little extra 
> for matching filters but it would be good to do some measuring.

One way is to use an audio spectrum program like Spectrogram which has been
used widely for setting up K2s and by some to look at their K3 IF response.
There are better, more accurate and/or higher resolution equivalents.  K9YC
used a professional program with high quality hardware to produce the
measurements he shared with us.

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.

73,
Ed - W0YK