[Elecraft] [K2] Low sensitivity with variable-bandwidth filter

[Bill Coleman]

Well, I think I finally got it sorted.

I replaced D1 and D2 on my KAT100. One of the diodes was good, the other was likely bad since I couldn’t get the SWR bridge to null, but I destroyed it while extracting it from the board.

New diodes are in machined socket pins, which will make them easy to replace (or test) later, if need be. SWR bridge calibration went swimmingly.

As for the filter problem, I did a CAL FIL and checked OP1 on LSB and USB, All four filters on CW and RTTY.

Other than a few minor tweaks, the only thing I ran into was FL1 on CW (which is a 1.0 filter) was about 200 Hz low. FL3 (0.16) was about 30 Hz high.

After the CAL FIL, the radio sounds normal again. I don’t believe I’ll do a full alignment.

Thanks for your assistance.

> On Jun 12, 2019, at 10:09 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Bill,
> 
> Yes, do the CAL FIL calibration first.  If that does not cure anything, then proceed with the rest of the alignment, but I doubt if that will help much - the K2 alignment is usually quite stable over time.
> The bandpass filter and other alignments are not going to change the relationship between the SSB filter and the CW filter - only CAL FIL will do that.
> 
> If you still have a problem after the full CAL FIL, you will usually find a problem in the CW filter bank - like a bad crystal (but that does not happen often).  Reflowing the soldering on the IF crystals on the RF Board may help.
> 
> 73,
> Don W3FPR
> 
> On 6/12/2019 8:23 PM, Bill Coleman wrote:
>> Yeah, this is looking more like a calibration problem.
>> 
>> I’m listening to W1AW code practice on 14.0475. As I cycle through the filters the S-units are roughly the same through OP1, 0.4 and 0.16. But on the 1.0 bandwidth, it is often 1-2 S-units lower. If I tune about 200 Hz lower, I get the same number of bars.
>> 
>> I’ll update you when I have a chance to do the calibration.
>> 
>> 
> 

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901