K2 SSB Receive issue

[KA1YMX]

I recently finished aligning my K2 with the spectrogram software and with the procedures from Elecraft. I am able to receive SSB on all bands except on 21m and 12m. The SSB signal is very distorted and sounds like the filter is not wide enough to receive the SSB signal.  I completed all of the alignments in the manual without any issues. I know I must have missed something small but cannot figure it out. Before I start to adjust anything on the K2, does anyone have any suggestions?

[Don Wilhelm-4]

  I am going to make 2 assumptions - correct me if they are wrong.
1) You do not have the KSB2 installed with its fixed 2.4 kHz width
filter, and you are attempting to use the variable IF filter at wide widths.
2) Your K2 has a serial number somewhere near 6800.

If those conditions are true, the 1SV149 varactors in your kit have a
greater capacitance range than with the older varactors.
What that means is that your wide filters (above about 1.00 kHz) are
much wider than indicated on the K2 display.  On one K2 I recently
aligned a filter indicated as 1.70 was actually 2.4 kHz wide.  That is
the most variation I have observed in many K2s that I have aligned, more
typically an indicated filter width of 1.90 would be about 2.4 kHz wide.

What that means is that the BFO frequencies listed in the manual will be
about correct for the LSB filters, but are nowhere near correct for USB.

The only way I know to correct this situation is to use Spectrogram to
measure the actual filter width.  Set the BFO for LSB about correct
first, then reduce the width of the filter to whatever width you would
like - I use 2.4 kHz for FL1, 2.2 for FL2, 2.0 for FL3 and 1.8 for FL4.  
Those are the Spectrogram measured widths, not the K2 indicated widths.

After setting the filter widths, then trim up the LSB BFOs to place the
upper "corner" of the left passband slope close to 300 Hz and then
switch to USB and adjust the BFO so the upper passband corner is
positioned also at 300 Hz.

You can find some information about using Spectrogram on Tom Hammond's
website www.n0ss.net and also in part 3 of the K2 Dial Calibration
article on my website www.w3fpr.com.

73,
Don W3FPR





On 1/15/2011 1:36 PM, KA1YMX wrote:
> I recently finished aligning my K2 with the spectrogram software and with the
> procedures from Elecraft. I am able to receive SSB on all bands except on
> 21m and 12m. The SSB signal is very distorted and sounds like the filter is
> not wide enough to receive the SSB signal.  I completed all of the
> alignments in the manual without any issues. I know I must have missed
> something small but cannot figure it out. Before I start to adjust anything
> on the K2, does anyone have any suggestions?
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[KA1YMX]

I am sorry I should have mentioned I have the KSB2 SSB board installed.  I  followed the K2 Dial calibration procedures on your website to verify everything is aligned properly and it is. I checked for SSB reception on 21m and 12m and the SSB audio is still distorted. All other bands work below 21m.

[Geoffrey Mackenzie-Kennedy]

This may or may not be relevant but low side mixing is used on 15m, 12m and
10m where distortion is heard, and high side mixing on the lower frequency
bands where distortion is not heard.

73,
Geoff
GM4ESD

KA1YMX wrote on Saturday, January 15, 2011 at 9:04 PM:

> I am sorry I should have mentioned I have the KSB2 SSB board installed.  I
> followed the K2 Dial calibration procedures on your website to verify
> everything is aligned properly and it is. I checked for SSB reception on
> 21m
> and 12m and the SSB audio is still distorted. All other bands work below
> 21m.


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[KA1YMX]

I shouldn't have used the word distortion. The SSB stations are completely unreadable, very similar to a narrow filter.

[Don Wilhelm-4]

  Is your reference to "21m" a typo instead of 20m, or are you referring
to the 21 MHz band which is 15m.
Are you choosing USB for the 20m, 17m, 15m, 12m and 10m bands?.
How does the LSB signals on 80m and 40m sound?

The sideband inversion Geoff mentioned is such that on 15m, 12m and 10m,
the actual sideband being used is the same as LSB on 80 and 40.  The K2
automatically accounts for the inversion, and displays the mode as USB
which is correct.

73,
Don W3FPR

On 1/15/2011 4:04 PM, KA1YMX wrote:
> I am sorry I should have mentioned I have the KSB2 SSB board installed.  I
> followed the K2 Dial calibration procedures on your website to verify
> everything is aligned properly and it is. I checked for SSB reception on 21m
> and 12m and the SSB audio is still distorted. All other bands work below
> 21m.
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[KA1YMX]

I used my K3 to transmit a USB/LSB on all bands except for 10m. The only two bands that I could receive a readable SSB signal was on 20m and 17m. I tried USB and LSB on all other bands and could not receive a readable signal. I used my S-Meter to adjust the frequency on the signal in which I did not have a readable signal and the peak of the signal on the K2 was about 2.2 khz below the indicated frequency on the K3.  I adjusted and verified the K2 is on frequency using WWV prior to performing this test so I know both the K2 and K3 are on frequency.

[Don Wilhelm-4]

  Go back to the filter alignment and look at the BFOs for each filter
(you may look either at the DAC values or at the frequency).  If the
settings for LSB are the same as you have for USB, then you have the
BFOs set to the wrong sideband.  Use 40 meters for this test so there is
no confusion about sideband inversion.

It would appear that you have the BFOs for USB correct, but not for
LSB.  The LSB DAC values (and the as a result the frequency) must be
lower than those for USB.  The dispaly in Spectrogram will look similar
whether it is LSB or USB, so if you were not conscious of the frequency
(or DAC value) during the process it is easy to set it to the wrong
sideband - it looks right, but it is not.

If you look at the frequency of the BFO used for OP1 as FL1, LSB will be
near 4913.5x and USB will be near 4916.5x.

That could also explain the frequency discrepancy when looking for the
frequency of a signal peak.

73,
Don W3FPR

On 1/15/2011 7:33 PM, KA1YMX wrote:
> I used my K3 to transmit a USB/LSB on all bands except for 10m. The only two
> bands that I could receive a readable SSB signal was on 20m and 17m. I tried
> USB and LSB on all other bands and could not receive a readable signal. I
> used my S-Meter to adjust the frequency on the signal in which I did not
> have a readable signal and the peak of the signal on the K2 was about 2.2
> khz below the indicated frequency on the K3.  I adjusted and verified the K2
> is on frequency using WWV prior to performing this test so I know both the
> K2 and K3 are on frequency.
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[KA1YMX]

The USB and LSB BFO for each filter was almost identical to each other. I used the BFO numbers in the K2 SSB manual as a starting point and used spectrogram to fine tune the filters. I am now able to receive readable SSB on all bands. I knew it was something I overlooked. Thank you for your help.