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

[Jim Brown]

On Tue, 19 Aug 2008 06:01:35 -0700, Mike Scott wrote:

>Could someone explain a method of measuring roofing filter offset? 
>I have spectrum analysis software. 

Once you've studied the manual thoroughly and learned to use the 
radio, it will become obvious. First, the FFT system must be set for 
high resolution scan rates. I use a professional audio FFT (EASERA 
SysTun) with band noise as the signal source and lots of averaging. I 
measured and stored plots of the DSP filters, then measured and stored 
again with the K3 set so that the roofing filter kicks in with the DSP 
filters set to be very broad band. Then I overlaid those plots. It's 
important to measure at the headphones output -- the Line Out can 
overload at relatively modest signal levels, as noted in the manual. 

These offsets are nothing more or less than manufacturing tolerances 
in the filters. Ain't no big thing, since the K3 can easily be 
adjusted to compensate. But it's wrong to deny that they exist. 

73,

Jim Brown K9YC