[Elecraft] K2: Various Receive Problems

[Jon Perelstein]

This is an update to a post I made in Nov 2008.  I've received a fair number
of off-board emails over the past 1-1/2 yrs asking me about the problem and
solution, so I figure I'll post the solution and save others from some
embarrassment.
 
My original problem was described as follows:
 
 
>>2. On receive, stations are either there or not there.  
 
>>In this case, if I hear a signal, I hear it at the same volume as I tune
across the signal's bandwidth.  The perceived signal strength simply does
not change.   
 
>>Along with this, there is no interference from adjacent signals.  I'm
always hearing the strongest station and only the strongest station at
whatever spot that my VFO is tuned to.    
 
>>3.  As I tune across a CW station's signal, there is no change in audio
frequency. 
 
 
Well, it's embarrassing to admit it publicly, but both of those problems
turned out to be user error (really really dumb user error).  I did not
understand the differences between digital tuning (like the K2 and K3) and
analog tuning.  More specifically:
 
With digital tuning, each incremental shift of the VFO jumps the tuning by
the set amount -- from one frequency instantaneously to the next frequency
without sweeping through the frequencies in-between.   Thus, for example, if
you have the rate set to 1KHz and are at 7035.00, a slight move of the VFO
to the right (clockwise) will result in your jumping to 7036.00 without
having heard any of the frequencies in-between.  

Compare that with analog tuning where you sweep through the frequencies so
that you hear all of them -- briefly, but you hear all of them.

In other words, tuning in a digital world is like tuning a television or
tuning a VHF FM mobile rig -- you're jumping from one frequency to another,
you're not sweeping through the frequencies between them.

For example, assume there are two CW signals out there:  a strong signal
centered at about 7036 and a weaker signal centered at about 7035, each with
a bandwidth of about 2.4KHz.  That means that the weak signal extends from
about 7033.8 to about 7036.2, and the strong signal extends from about
7034.8 to about about 7037.2.  If you're tuning with a 1KHz RATE, you
probably won't hear anything at 7033.10.  Turn the VFO slightly and you're
at 7034.10 where you'll hear only the weak signal since you're already
within its bandwidth but not within the bandwidth of the strong signal.
Tune again (to 7035.10) and you'll only hear the strong signal because it
will overwhelm the weak signal.  Tune again (to 7036.10) and you're again
hearing the strong signal.  Tune again (to 7037.10) and you're again hearing
only the strong signal, especially because you're outside the bandwidth of
the weak signal).  Tune again (to 7038.10) and you won't hear anything.
Thus, it winds up sounding just like what I had described in my original
post.

Note that in the example above, you've only listened to 6 specific
frequencies (7033.1, 7034.1, 7035.1, 7036.1, 7037.1 and 7038.1).  You have
no idea what's happening at any of the frequencies in between.  You haven't
listened to them or swept through them.  You have completely jumped over
them.
 
And just to make matters worse, the brain tries to interpret the sounds at
those spots as being identical volume.  As does the AGC.

The effect doesn't appear to happen with a tuning rate of 10Hz because
you're going in such small increments that your brain interprets it as
continuous sweep tuning.  As you tune from low to high, you'll hear the weak
signal start to come in and rise in volume, then you'll hear the strong
signal start to come in, then you'll hear the strong signal overwhelm the
weak signal, then nothing but strong signal, and then you'll hear the strong
signal start to "fade" out as you tune past it. Compare that with tuning at
a 1KHz rate where things seem to magically appear and disappear. 

When I first started working with the K2, I had never before experienced
digital tuning (at least not on an HF rig) and thus I was expecting
something along the lines of what I was used to in my old Swan 350 and in my
FT-897 -- that tuning was sweeping through frequencies rather than jumping
from frequency to frequency.  In my expectations, the RATE on the K2 was
setting how fast I swept through the frequencies rather setting how much I
jumped between frequencies.

 
*****
 
Hope this helps
 
Jon
KB1QBZ