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

[Don Wilhelm]

Bill,

Congratulations, it sounds like you have achieved success.

Once set the K2 alignment usually remains stable for a long time. If it 
ain't broke, don't fix it!

Don W3FPR

On 6/17/2019 10:36 AM, Bill Coleman wrote:
> 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
>
>