[Elecraft] K2 ALC problem

[Don Wilhelm]

Gary,

I would expect two possible causes.
One is the carrier balance adjustment.  Use a band below 21 MHz when 
adjusting and adjust for LSB first.  If you have an oscilloscope, the 
procedure is easy - connect a dummy load to the K2 and connect a paddle 
or straight key to the key jack.  The oscilloscope is to measure the RF 
output voltage, so connect it across the dummy load with a 10x probe and 
set the vertical sensitivity to its greatest setting.  In LSB mode, 
close the key (which activates PTT) and adjust the carrier balance for 
minimum RF.  That setting should occur close to the center of the 
trimpot.  Then check USB  If the USB carrier is greater than that for 
LSB, adjust the pot a very small amount to see if you can reduce  the 
carrier.  You may have to make some compromise to get the amount of 
carrier the same between LSB and USB.  Note, if you use this method, do 
not connect a microphone to the K2 and you do not have to set the menu 
for "SSBA bal".  You can use a separate receiver to detect the minimum 
carrier in place of the oscilloscope as indicated in the KSB2 manual, 
but I suggest using the key to activate the PTT circuit rather than 
plugging in a microphone.  A mic with its PTT button pressed can pick up 
residual noise and cause a false indication.  This is easier done than 
to write about it.

The second possible problem is alignment of the SSB filter.  Use 
Spectrogram and set the BFO to position the OP1 filter passband between 
300 Hz and 2600 Hz markers (use 300 and 2300 if you have the 2.1kHz 
filter width or 300 and 2800 if you have the 2.6kHz filter width).  
Center the passband between the two markers.  Check both LSB and USB.

If you moved the SSB passband in the step above, re-visit the SSB 
carrier balance adjustment.

If those steps do not correct the imbalance between LSB and USB, you may 
have some fault on the KSB2 board.  A very small difference may exist, 
but not to the extent that you have indicated.

73,
Don W3FPR

Gary D Krause wrote:
> Hi,
>
> I've noticed that my power output on 40 meters LSB is a lot higher 
> than expected.  I get four to five bars or more on the peaks in the 
> ALC mode.  I even got a high current reading last night and I then 
> turned the power back from 12 watts to 10.  I get 4 to five bars even 
> at five watts.  It didn't make much difference and I've found that I 
> need to hold the mic further away. I switched to USB on 40 meters and 
> it looks fine.  It looks good on the higher USB frequencies also.  
> I've noticed that it is around 2 to three bars on 80 meters LSB which 
> is normal according to the manual.
>
> I'm wondering if it could be a carrier balance adjustment?  Any ideas 
> would be greatly appreciated.  Everything else appears normal.  I've 
> checked all solder connections on the SSB board several times and 
> re-flowed the connections I considered suspect.
>
> Thanks,
> Gary, N7HTS
>
>
>
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