[Elecraft] K2 - Interpreting the results of CAL FIL & Questions

[Bill Coleman]

In building K2 #2548, I first set the BFO according to the manual 
numbers, as specified in the Table 8-1. When I did so, the radio sounded 
somewhat odd. The default numbers seemed to sound better in the 
headphones.

Since I was about ready for final assembly, I decided to re-do the BFO 
calibration using MacCRO (Think Different!), and a noise source. (I know 
where N0SS got his design - it matches an RX noise bridge I built from 
the 1991 ARRL handbook, but there is no 555 timer). Looking at the 
spectral display, I found that the normal CW peak was somewhere around 
1.3 kHz, and the CW REV mode had it down lower.

After spending a half-hour making adjustments, I wondering if I'm doing 
it right. I have my CW filters set up with standard bandwidths of 1.5, 
.7, .4 and .1. SSB is also standard (2.2, 2.0, 1.8, 1.6 ?), according to 
table 8-1.

Looking at the spectral display, the bandwidths larger than .7 have 
considerable asymmetry to them. This is really noticable on SSB, as the 
"color" of the noise through the USB and LSB modes is quite different. 
(And it inverts above 17m) Is this normal? 

I figure the USB and LSB filter shape will be improved with the SSB 
option. (I have the KSB2, just haven't built it yet)

Another question I have regards how different the BFO settings are in 
each filter. How does the K2 ensure that the transmit carrier is properly 
sent through each passband? In other words, if one matches the beat note 
of a CW signal and then switch filters, wont the TX frequency change?

I noticed that when I changed modes the apparent frequency of the K2 
shifted considerably between CW, LSB and USB. The LSB / USB shift I can 
understand. I suppose I'm used to the Kenwood TS-430S -- changing from CW 
to USB has no effect on the received frequency (although the dial does 
shift by 800 Hz). Is this shifting normal? (I remember the old Heathkit 
SB-301 had a special LMO circuit so that the LSB and USB had a common 
zero beat)

Also, during construction, I had to write down the number on the envelope 
for the 7 crystal set (mine was 3.9). In the instructions, it said this 
number would be used later for calibration. However, it wasn't ever 
mentioned again.

Now, I have the KSB2, and it has a different set of crystals (perhaps 
with a different number). Looking at the KSB2 manual, this number is used 
to adjust the OP1 filter. 

So, where does one use the number for the variable-bandwidth CW filter?





Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901