[Elecraft] K2 / KPA ALC problem.

[Don Wilhelm]

Chris,

A few things come to mind.  Does your KSB2 have the KI6WX increased RF 
gain mod installed?  If so, you may have to add some additional changes 
to the KSB2 to control the ALC.  Change R9 to 15k and cut the trace 
between P1 pin 6 and Q1 base and insert a 1K resistor (you will have to 
mount the resistor vertically).
Even without the KI6WX KSB2 mods, this change may help your situation.

The other thing is the value of R98 on the bottom of the RF Board. The 
nominal value is 270 ohms, but the optimum value depends on the gain of 
the RF transmit chain.  With the KPA100 installed, the value may have to 
be increased to maintain optimum ALC action.

There is a K2 app note describing the process to determine the optimum 
value of R98 for any particular K2 (it will very from K2 to K2).  In 
short, temporarily replace R98 with a 2k (or greater) pot, and adjust 
the value until the power begins to drop on 10 meters. Remove the pot 
and measure its value.  Replace R98 with a standard resistor value lower 
than the resistance of the pot.

Hopefully one or both of those mods will solve your problem.

73,
Don W3FPR
On 12/2/2013 8:22 PM, Chris Kimball wrote:
> I'm getting reports that my digital mode Olivia 8/500 signals are distorted.
> Usually, the comments fall into two categories: 1) overdrive  2) audio
> compression on.  I know that the audio compression is set 1:1 (off). And
> I've tried to prevent overdrive by the method suggested by Don Wilheim,
> W3FPR, in his response to my earlier posting of Apr 14, 2013.  That is,
> adjust the input levels so that no bar appears in the K2 ALC bar graph.
>
> But I've had a strange problem with the ALC. When the power level is 10 W or
> less (and the KPA is in-line, but off) I'm able to set the input levels so
> that the ALC bar indicator shows no bars AND a signal is output.  When I
> increase the power level to 11 W (KPA is on), the exact same settings yield
> an unwanted, single ALC bar indication.  If I then decrease input levels,
> the ALC bar disappears, but, alas, there's no signal output.
>
> For power levels greater than 10 W, that is, with the KPA on, I can't get
> any reliable output unless at least one ALC bar is showing.
>
> Listeners say the less than 10 W signal sounds fine.
>
> As I understand it, the ALC stays entirely within the K2, that is, it
> doesn't go to the KPA.  Control, DC, and RF lines are short and the system
> is well grounded.
>
> Suggestions would be appreciated.
>
> Chris
> NQ8Z
>
>
>
>
>
>
> --
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