[Elecraft] K2 LSB Modulation issue

[Don Wilhelm]

  Michael,

First a comment - why use SSB FL4 set to 700 Hz width for PSK and have 
to remember to turn the compression off when using digital modes?  It is 
much easier (IMHO) to go to the secondary menu and turn the RTTY filter 
set on.  That gives you a compression setting independent of that used 
for SSB - just set it to 1:1 for the RTTY filters and be done with it.

I usually set RTTY FL1 the same as SSB FL1 OP1 filter and the BFOs the 
same.  That gives you a full width passband for normal point and click 
in the waterfall.  Then I set FL2 to 1.00, FL3 to 0.70 and FL4 to 0.40 
to give narrow RTTY filters when QRM shows up - yes you have to tune to 
the filter center with the VFO, but at least you can continue 
operating.  Center the narrow RTTY filters at 1000 Hz, and easy number 
to remember and it works well with MMTTY when the mark frequency is set 
to 915 Hz.

Now on to your question - yes, that is a problem - the low end of your 
BFO range is too high.  You can increase both C173 and 174 keeping the 
ratio close to 3:1, or you can try an easier fix first, solder a small 
value capacitor from the juction of the crystals to ground (U11 pins 6 
and 3 maje nice anchor points).  I would not exceed 27 pF with this 
added capacitor because it can decrease the BFO RF voltage level.  Check 
both the high and low end of the BFO range after making this change (see 
manual page 62).  The high must be greater than 4916.3 and the low less 
than 4912.7.  If you cannot achieve the correct range with this single 
capacitor addition, you will have to change both C173 and C174.  I would 
try 100 pF and 330 pF to see if that brings it into range.

You may want to write down the frequencies (not the DAC values) of the 
BFOs that you already have set because all the BFO settings will be 
shifted and you will have to do the filters over again.

73,
Don W3FPR

On 10/11/2010 6:33 PM, Michael Jensen wrote:
> Hi Don
>
> Thanks for your answer.
>
> I have now done a realignment using Spectrogram as I did originally. I
> believe using the exact same instruction.
>
> I might have asked this 4-5 years back but maybe without prober explanation,
> any way I do not recall the answer.
>
> Setting the LSB FL4 for PSK to a bandwidth of 0.7 I struggle to reach a
> center of 1KHz. I can get to about 800 with a BFO of 4912.99 and a dac of 16
> going further then that the signal fade. Is that a problem....??
>
> The tuned values for FL2 OPT1 are 4913.52 dac 001 and FL3 of 1.8 is 4912.94
> dac 001...
>
> I have not yet had the possibility for some one that know me to listen to my
> tx audio, so I could tune FL1
>
>
> For reference the setting on USB are FL2 OPT1 4916.36 dac 212, FL3 1.8
> 4915.90 dac 195 FL4 0.7 4915.08 dac 164
>
>
> Thanks in advance
>
> 73 de OZ1BZJ
>
> Michael
>
>
>
> -----Oprindelig meddelelse-----
> Fra: Don Wilhelm [mailto:w3fpr at embarqmail.com]
> Sendt: 11. oktober 2010 00:49
> Til: Michael Jensen
> Cc: elecraft at mailman.qth.net
> Emne: Re: [Elecraft] K2 LSB Modulation issue
>
>    Michael,
>
> I suspect that the BFO for LSB is not correctly for your KSB2 OP1 filter.
> First check to be certain the SSB FL1 is set to OP1.  The BFO frequency
> for LSB using the OP1 filter will be between 4913.48 and 4913.65
> depending on your particular filter center, and the USB BFO will be in
> the vicinity of 4916.5.  You can check with the internal frequency
> counter probe in TP2, enter CAL FIL and tap the BAND- button.
>
> Then go to my website www.w3fpr.com and read part 3 of the article
> dealing with K2 Dial Calibration - that is the section that explains the
> filter setting using Spectrogram.
> If you do not have a copy of Spectrogram and or need information about
> how to set it up on your computer, download it from Tom Hammond's
> website www.n0ss.net.
>
> If you have not set up your K2 filters before using Spectrogram, you may
> want to align all your filters.
>
> 73,
> Don W3FPR
>
>
> On 10/10/2010 5:36 PM, Michael Jensen wrote:
>> Hi all
>>
>>
>>
>> I have noticed an issue on my trusty K2 #5111.  Might have been there
> since
>> I build it several years ago or it might have come during the years
>>
>> The issue are the modulation on LSB. The audio are not very good and do
>> sound "funny" Could maybe be described as nasal or some one knowing my
> voice
>> call it "like the audio was being frequency modulated".
>>
>> USB are ok or at least so much better that no one notices.
>>
>> There are no difference between running high power or low power and have
>> tested using different power supplies.
>>
>> The reason for going un detected is that I in the past not often was below
>> 20 on SSB. When I used 40 or 80 it was mainly PSK but running USB. So no
>> issue seen. When I was made aware of the issue I first put the blamed on a
>> power supply for my PA as beeing the reason. (the magnetic field issue
>> discussed here several years back). Now having tested for that it do not
>> seem to be the problem.
>>
>> Any of you that would have experience or comments on a TX audio issue that
>> effect only LSB.
>>
>>
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