[Elecraft] [K2] Trouble dialing in KAF2's AF2

[Don Wilhelm]

  Brian,

You are being deceived by using a single signal source.  It is very 
difficult to adjust a filter using a single signal because you have to 
plot the shape of the passband using many data points obtained by tuning 
the VFO through the signal very slowly.  A noise source and Spectrogram 
will display the passband in its entirety on the screen.

Set the K2 for a 700 Hz wide IF filter, then connect a noise source - an 
antenna on a dead band with the preamp on will do.

What you are looking for is to narrow the width of the passband as shown 
on the Spectrogram display.  First switch to AF1 and you should see a 
peak in the passband display (it would have had a flatter top before 
switching on AF1).  Adjust the lower pot to put that peak in the 
passband display at your chosen sidetone pitch.
Having done that, turn on AF2 and adjust the upper pot for the same 
thing - also you should see the passband narrow more substantially at 
the top and the skirts will be a little steeper than they were with only 
AF1 in the circuit.
Go back to the lower pot and try to make the peak even more pronounced 
and the skirts steeper.  Alternate between the lower and upper pots 
until you have it the best it can be.  You should only have to move the 
pots a very small amount to see a change.

73,
Don W3FPR

On 6/5/2011 3:42 PM, Brian - N5BCN wrote:
> Hi all,
>
> I aligned the KAF2 using a XG1 and Spectrogram.  I tried the broadband noise
> method, but found the line for the peak very coarse, it seemed the XG1 peak
> was much more stable and easier to discern.  Regardless, I thought I had R1
> and R2 really dialed in for both AF1 and AF2.
>
> AF1 seems to perform as it should: ever so slight drop in signal strength,
> but nice audio filtering.  AF2, however, causes a significant drop in signal
> strength.  The instructions suggest that AF2 should have no drop, and, if
> anything, a slight increase in gain.
>
>