[Elecraft] K2 filter alignment

[kt5x at cybermesa.com]

Responding to N2PD's request for help with filter alignment...

I have a different approach than that used by anyone else I have heard from, 
so I thought I would share it.  But do know that absolute precision is not 
possible as the resolution for alignment is limited.  the best you can do is 
quite close.

It is a good idea to have warmed up your radio for an hour before doing this, 
and have a stable shack temperature as well.

You are going to use MATH, fancy that, in this approach.  Let's say you have 
chosen 600 cycles as your listening pitch.  Move through the menu until you 
have the BFO frequency on the screen.

Now, with no antenna, but gains turned up, close your eyes and tune through 
zero-beat.  Find the absolute zerobeat.  It all depends upon finding the 
zerobeat accurately, so take your time.  Now, open your eyes.

Record the BFO frequency.  Subtract your chosen listeing frequency for CW 
regular and add for CW reverse.  For example, my chosen frequency is 400 
cycles.  My center for my first filter is 4913.78.  So I subtract or add 40 
after the decimal (see, resolution is to plus or minus ten cycles, and 
further, you sometimes can't get the exact number you want either because it 
will flicker between two numbers, turn just a little and it flickers between 
the next two).  So my CW regular is 4913.38 and CW R is 4914.18.

After setting these two BFO frequencies for CW regular and CW reverse, go 
back and forth between them to see if they are the same frequency.  IF you 
indeed found zerobeat, they will be very close.  If they are not close, you 
missed zerobeat.  In that case, equalize them by changing both either one 
number higher or one number lower, until they are indeed balance, very close 
to a match.

Go on to the next filter.  When the tone matches between CW regular and CW 
revers AND they are exactly double your chosen listening frequency apart from 
one another, they are set as closely as it is possible to set them.

I find that the settings are temperature dependent.  In the winter ambient 
shack temperatures are as much as twenty degrees (60) lower than in summber 
(80).  That difference moves the zerobeat BFO frequency a little and that 
moves the regular and reverse frequencies apart since they are no longer an 
equal distance from zerobeat.

73

Fred - KT5X