[Elecraft] "worse carrier rejection" when KPA100 active?

[Don Wilhelm]

Oleg,

Unless you changed the time-base on your oscilloscope between the 
photos, I calculate that the period of the ripple is close to 0.11 ms 
which would mean a ripple frequency near 9000 Hz., but you will have to 
tell me how your'scope time base is set.
It may be possible for your light source to cause that effect if your 
light is a florescent type.  An incandescent light would produce that at 
the 50 Hz line frequency.  Put some black tape over the PA transistors 
as a test and see if the ripple is reduced.

You will likely have to probe around in the KPA100 circuit to see where 
it originates.  If the PA transistor base has a clean signal, and your 
DC Supply is clean, then I do not have a good answer.
OTOH, if the ripple is present at the PA transistor base you should 
probe further to see if it is coming from the bias supply (U7B and Q4) 
or from somewhere in the T/R switch area.

If you have the KPA100 mounted to the base K2 when you are doing this 
test, be certain the shield is fully in place and that the KPA100 ribbon 
cable and speaker cable are dressed well away from the KSB2 board.  
Remove the right side panel and tuck those cables up into the area 
between the KPA100 heat sink and the top of the Control Board.

73,
Don W3FPR


dl0tuh wrote:
> Don, thanks for your reply!
>
> I repeated my tests with a 12V 7Ah battery connected to KPA100 power
> terminals as the only power supply of K2. And, to eliminate 2tone
> complexity, I only used single 1900 Hz tone.
>
> Unfortunately for me, there is no change compared to 20A PSU used yesterday.
> 10 watts are ufb (photo 3), but 11 watts signal looks much like an AM signal
> (photo 4). The frequency of the envelope on photo 4 is the tone frequency
> (well, may be +- 50 or 100 Hz), I tried changing it.
>
> (3) http://www.mydarc.de/dl2ipu/kpa100/one_tone_10_watt.jpg
> (4) http://www.mydarc.de/dl2ipu/kpa100/one_tone_11_watt.jpg
>
> I'm not expecting 50 Hz buzz from my sound card, that one I would see at 10
> watts, too. Neither I'm expecting any ripple from a battery. Out of ideas by
> now...
>
> 73! Oleg
>
> P.S. Remember photo-effect of power transistors of KPA100, producing abt
> 0.2V where 0V should be during DC checks? I have a very strong light above
> my table, hi
>   
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