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K2 SSB ALC Problem

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Sanjin Tajic, E71DX

K2 SSB ALC Problem

Hi All,

I have a K2 which I bought used. I never really used it on SSB but from time to time would like to.

The problem is when I transmit (Mic is the Elecraft MH2) I get very hard ALC action which jumps to full ALC scale reading.

I tried to "inject" (via the Mic in a quiet room) a constant modulation and even with this "constant" source I get a very erratic ALC action.

I get this ALC action with all Mic-gain and Mic-comp settings - more or less ALC respectively.

In all cases the actual Power-out is as it should be and I have no problems with the power control neither in CW or SSB.

This was present from the first day I got it but till now did not really bother me much.

Options installed are: KSB2, K160RX, KNB2, KAF2, KIO2, KAT2, K60XV, KBT2.

Thanks in advance for all tips!

Sanjin, E71DX

Don Wilhelm-4

Re: K2 SSB ALC Problem

Sanjin,

What setting do you have for the SSBA menu parameter - for the MH2, it
should be set at 1.

Does your K2 have any additions to the KSB2 board, such as the KI6WX
increased gain mod? If you don't know, open the K2, remove the KSB2
board and check for an additional transistor mounted on the board - it
will be near U5 and could be either on the top or bottom of the board.
If that mod is present, *and* especially if you have the KPA100 (either
internal or external), there are changes to the ALC circuit on the KSB2
board that must be made to keep from "slamming" the ALC.

There is also the possibility that you have an ALC problem on the KSB2
board - if it is a very early KSB2 board, there were some changes made
to improve the IMD for data modes that changed the ALC component
values. Download the current KSB2 manual from the Elecraft website and
compare the values of the components in the lower left corner with the
values you have on your KSB2 board. That is one downside to buying a
used K2, you can never be certain which changes have been installed
without inspection, unless the seller provided you with complete and
detailed information about changes.

73,
Don W3FPR

Sanjin Tajic, E71DX wrote:

> Hi All,
>
> I have a K2 which I bought used. I never really used it on SSB but from time
> to time would like to.
>
> The problem is when I transmit (Mic is the Elecraft MH2) I get very hard ALC
> action which jumps to full ALC scale reading.
>
> I tried to "inject" (via the Mic in a quiet room) a constant modulation and
> even with this "constant" source I get a very erratic ALC action.
>
> I get this ALC action with all Mic-gain and Mic-comp settings - more or less
> ALC respectively.
>
> In all cases the actual Power-out is as it should be and I have no problems
> with the power control neither in CW or SSB.
>
> This was present from the first day I got it but till now did not really
> bother me much.
>
> Options installed are: KSB2, K160RX, KNB2, KAF2, KIO2, KAT2, K60XV, KBT2.
>
>
> Thanks in advance for all tips!
>
> Sanjin, E71DX
>

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Sanjin Tajic, E71DX

Re: K2 SSB ALC Problem

Hello Don,

thanks a lot for taking you time!

I have SSB-A set to 1 but I can get a lot ALC action very easily.

My KSB2 Board is a Revision D with firmware 1.08 and there is no additional transistor around U5 on the top or the bottom side of the board. I do have an KPA100/KAT100 in an EC2 enclosure.

I will check the components as good as I can in the morning.

Once more, thank you for the help!

73, Sanjin
E71DX

Peter, DL2FI

Re: K2 SSB ALC Problem

Sanjin,

I have seen this in some seldom cases when KPA100 was used. Absolutely
successful is following Mod I got from Elecraft Support some time ago:

You need to change R9 to 1.5K on the KSB2 if the ALC
is not able to keep the SSB RF output under control.

Then also cut the PCB trace to the base of Q1,
and solder a 1K resistor across the cut.

This helped, even with the fully modified SSB Board as we do it in Germany
since some years (we use a compilation of some SSB Mods which give a
wonderfull strong and clean Modulation in total) Several K2 on DXpeditions
are using this Compilation of Mods. You will find our SSB Mod Compilation
here: http://www.qrpproject.de/UK/elecraft_k2.htm

72/3 de Peter, DL2FI

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Sanjin Tajic, E71DX

Re: K2 SSB ALC Problem

Hello Peter,

I have seen your suggested mod in the Summary of K2 Mods Document on your Site before but was not sure if I should do it since the behaviour is the same weither the KPA100 is connected or not.

Dankeschön für deinen Input!

73, Sanjin
E71DX

Peter, DL2FI

Re: K2 SSB ALC Problem

Sanjin,
problem occured seldom with K2/KPA100
amd much more seldom with K2/allone

But Gary´s Mod helped in all cases :-)

72/3 de Peter

> -----Ursprüngliche Nachricht-----
> Von: [hidden email] [mailto:[hidden email]]
> Im Auftrag von Sanjin Tajic, E71DX
> Gesendet: Montag, 9. August 2010 15:13
> An: [hidden email]
> Betreff: Re: [Elecraft] K2 SSB ALC Problem
>
>
> Hello Peter,
>
> I have seen your suggested mod in the Summary of K2 Mods Document on your
> Site before but was not sure if I should do it since the behaviour is the
> same weither the KPA100 is connected or not.
>
> Dankeschön für deinen Input!
>
> 73, Sanjin
> E71DX
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-SSB-ALC-
> Problem-tp5387387p5388864.html
> Sent from the [K2] mailing list archive at Nabble.com.
> ______________________________________________________________
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Don Wilhelm-4

Re: K2 SSB ALC Problem

In reply to this post by Sanjin Tajic, E71DX

Sanjin,

Those resistors that Peter mentioned are the same changes to the KSB2
ALC circuit that I was referring to.
However, since your KSB2 has no additional gain modifications, I would
prefer that you determint that there is no other problem before making
those changes. I suggest the following steps.
Try operating into a dummy load - if the problem goes away, you have a
problem with RF Feedback.
Operate CW into a dummy load and view the RF level output with the
requested power set to 4 watts with an oscilloscope and a 10X probe.
The RF peak to peak value should be close to 40 volts. If there are
spikes in the RF output or there is substantially more or less than 40
volts peak to peak, then there may be a problem with the power
measurement circuits or the keying circuits.

Again, I would strongly suggest that you do those tests before
arbitrarily applying those changes.

73,
Don W3FPR

Sanjin Tajic, E71DX wrote:

> Hello Peter,
>
> I have seen your suggested mod in the Summary of K2 Mods Document on your
> Site before but was not sure if I should do it since the behaviour is the
> same weither the KPA100 is connected or not.
>
> Dankeschön für deinen Input!
>
> 73, Sanjin
> E71DX
>

Sanjin Tajic, E71DX

Re: K2 SSB ALC Problem

Hello Don, hello Peter,

I tried to transmit in a dummy load before the effect was the same. In fact I did almost all the testing with a dummy load.

Just tried what you suggested, set requested power to 4 Watts and transmitted CW in a 20 W dummy load through my Wattmeter - I do not have an Oscilloscope. Anyway, power out is 4 Watts as requested from 160 through 10m and the reading on the K2 display is matching with the Wattmeter.

73, Sanjin
E71DX

Don Wilhelm-4

Re: K2 SSB ALC Problem

Sanjin,

In that case, certainly try the resistor changes. The change is
reversible. If the SSB power out is not up to what it should be after
the change, then you will know that there is some other problem.
The K2 LED bargraph is almost as fast as an oscilloscope display - after
the change, check the ALC indication and then place it in RF display
mode - you should see the bargraph flicker at the peak power level. If
you need a reference level, press TUNE and it will show the CW level.
The SSB signal should peak up to that same level.

73,
Don W3FPR

Sanjin Tajic, E71DX wrote:

> Hello Don, hello Peter,
>
> I tried to transmit in a dummy load before the effect was the same. In fact
> I did almost all the testing with a dummy load.
>
> Just tried what you suggested, set requested power to 4 Watts and
> transmitted CW in a 20 W dummy load through my Wattmeter - I do not have an
> Oscilloscope. Anyway, power out is 4 Watts as requested from 160 through 10m
> and the reading on the K2 display is matching with the Wattmeter.
>
> 73, Sanjin
> E71DX
>

Sanjin Tajic, E71DX

Re: K2 SSB ALC Problem

Hello Don, hello Peter,

I tried the mod suggested by Peter but it did not really help. It seems to me that the ALC action is now somewhat better without the KPA100 attached but I am still not really sure about that - will check again.

Don do you have any other suggestions what I could try to do?

Thanks for the help,

Sanjin
E71DX

Don Wilhelm-4

Re: K2 SSB ALC Problem

Sanjin,

You may have some problem with the K2 VRFDET circuit - make certain the
power displayed by the K2 during a TUNE is close to the actual power
being developed. Do that both with the base K2 (no KPA100 physically
attached), and with the KPA100 attached.
If the actual power from the KPA100 does not match the power displayed,
you should balance and calibrate the wattmeter in the KPA100.

Given that your symptoms indicate that there is too much audio drive to
the KSB2 board, and also the fact that you bought this K2 used, look
carefully for something like a microphone preamplifier in the K2. One
easy way to tell if there is anything in the mic input path is to check
continuity between the AF Pin on the mic connector (pin 1 for Elecraft
microphones) and pin 5 of P1 on top of the KSB2 board. If there is not
direct continuity there, someone has put something in the path.
Also check the value of R14 (1k) and R15 (180 ohms) on the bottom of the
KSB2 board.

Stretching my mind for some other things - Do you have some source of
low frequency rumble in your hamshack? That low frequency audio could
be picked up by the microphone, and overwhelm the audio input. You
might change C34 to 0.47 uF and C32 to a capacitor in the 0.0033 to
0.005 uF range to reduce the low frequency audio. Many have made that
change and are quite pleased with it (I am one of those).

With the KPA100 attached, how long does it take the power to settle down
to 20 watts during a TUNE. It should take 30 seconds to a minute. If
it settles faster than that, look on the bottom of the RF Board for the
values of R98 and R99. If vastly different than the standard 270 ohms,
change them back until you have this problem under control. You may
want to optimize the value later after this problem is solved. (these
resistors normally have nothing to do with your problem, but if they are
way off the optimum value for your K2, strange things can happen).

I certainly wish you had an oscilloscope. Is there any chance that you
can borrow one?

73,
Don W3FPR

Sanjin Tajic, E71DX wrote:

> Hello Don, hello Peter,
>
> I tried the mod suggested by Peter but it did not really help. It seems to
> me that the ALC action is now somewhat better without the KPA100 attached
> but I am still not really sure about that - will check again.
>
> Don do you have any other suggestions what I could try to do?
>
> Thanks for the help,
>
> Sanjin
> E71DX
>