[Elecraft] KPA100 R 19 R20 question

[Dr. Werner Furlan]

hi Don, 

some questions I can answer now, some I have to look at in the "lab".

On 27 Nov 2007 at 6:20, Don Wilhelm wrote:

> The KPA100 does not distinguish between CW and SSB - input RF is input
> RF and it operates in a linear curve with a gain of approximately 10
> dB, so 10 watts in will produce 100 watts out and 2 watts in will
> produce 20 watts out and everything proportionally in  between.

ok. Looks like my problem is only in SSB mode. 

> How does your base K2 behave in SSB mode?  Does it produce 10 to 15
> watts output under similar conditions?

yes it does. The base K2 has a good SSB signal and works fine all over the 
range of 1-15 Watts (10W on 10m Band)

> I believe your problem may be either an ALC  problem on the KSB2 board
> or an RF feedback situation.

both seems possible to me. 

> First, I need to ask if you have any mods to the KSB2 board?  

yes - I have modifications. I have made all modifications recommended in 
this pdf:
http://www.qrpproject.de/Media/pdf/ZusammenfassungMods.pdf

it is in german, but I think you can understand it without knowledge of 
german when you see the circuit diagrams.

> Specifically the KI6WX Increased Gain mod.  If that mod is present and
> the KPA100 is added, the KSB2 ALC circuits may be overdriven.  There
> is a fix that can be added, or the mod can be removed to restore
> normal operation.

I would like to make a fix if necessary, without loosing the good modulation 
in qrp SSB.

> Even without the KI6WX mod, there still may be a problem in the ALC
> area of the KSB2 board, but it will likely be found to be a bad solder
> connection or an incorrect component (check the resistor values).  How
> does the LED Bargraph behave when the problem arises?  If it goes full
> scale in RF mode and lights many bars in ALC mode, then check the KSB2
> board ALC section carefully.

would this also be in QRP mode?
 
> There is also the chance that you have RF feedback into your
> microphone circuits.  That will not usually happen if you operate into
> a dummy load, but will show up when you are connected to an antenna. 
> If this is the case, the proper cure is to correct the RF feedback
> situation at the antenna, but in difficult situations, ferrites on the
> microphone lines can help somewhat.  If you have a data mode/soundcard
> interface connected, remove it and check without it.  The interface
> and its cabling produce additional cables and may be more susceptible
> to RF pickup than a microphone cable alone.  You may also want to
> ground the shell of your microphone jack if you have not done that
> already.

I'll check it again with sending into a dummy load. 
I'll also check it without the EA3BLQ digital board.
What do you mean by grounding the shell of the microphone shell?
Is it on the K2 or on the microphone cable?

I have another question about S-meter calibration with the Elecraft s-meter 
calibrator. Do you set the S0-S9 limits with preamp enabled or disabled?

73! de Werner
OE9FWV

--  
Pas de panique, Ca sera pire.



PGP-Key: <http://www.qsl.net/oe9fwv/furlan.asc>
Fone +43 5522 75013
Fax +43 820 555 85 2621
Mobile      +43 664 6340014