[K2] ALC and power control on 40m SSB in K2/100

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[K2] ALC and power control on 40m SSB in K2/100

VK7JB
Hello again folks,

Sorry about the barrage of posts from me. Just playing with my K2/100 #6998.

I've noticed that when operating in SSB  on 40m, requesting any power 15-20 W and up will always give me 100W+ output, measured into a dummy load.  Voice peaks are higher and result in Hi Curr warnings occasionally.  I can reduce the power above this threshold only by changing SSBC to 1:1 (normally run at 2:1 with my MH-2 mic) and winding the power out back to just on 11 W.

CW and TUNE modes - all OK:  power requested and power output track very well on all bands, including 40m.

Bands above 40m on SSB are not affected -  I mostly work 20m SSB and haven't noticed the power tracking issue there.  ALC seems to control the power out well there.

I suspect the Tx chain gain on 40m is too high for the ALC to manage when in SSB.  

Is there any way of making the ALC more aggressive on 40m SSB, without affecting the other bands too much?  I remember seeing a previous post about this somewhere but haven't been able to find the details again.

Any suggestions?

73,

John
VK7JB
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Re: [K2] ALC and power control on 40m SSB in K2/100

Steve Kavanagh
>Is there any way of making the ALC more aggressive on 40m SSB, without
>affecting the other bands too much?  I remember seeing a previous post
>about this somewhere but haven't been able to find the details again.

>Any suggestions?

>73,

>John
>VK7JB

John:

You probably have the diagnosis exactly right....this is a fairly common problem with K2/100s. Try these links for more info:

http://elecraft.365791.n2.nabble.com/Re-SSB-Power-control-and-KPA100-td444463.html#a444463

http://elecraft.365791.n2.nabble.com/K2-100-SSB-Power-Control-Problem-td384633.html#a384633

73,
Steve VE3SMA



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Re: [K2] ALC and power control on 40m SSB in K2/100

VK7JB
Steve, thanks.

I'll investigate the suggested mod to the KSB2.  Have you had to do this mod
yourself?  Did those resistor values work out about right for you (1k0 and
1.5k)?   Did the mod significantly affect the ALC action on higher bands?
I don't want to scarifice too much power out on 20m.

Thanks for the information.

73,

John
VK7JB

> John:
>
> You probably have the diagnosis exactly right....this is a fairly common
> problem with K2/100s. Try these links for more info:
>
> http://elecraft.365791.n2.nabble.com/Re-SSB-Power-control-and-KPA100-
td444463.html#a444463
>
> http://elecraft.365791.n2.nabble.com/K2-100-SSB-Power-Control-Problem-
td384633.html#a384633
>
> 73,
> Steve VE3SMA
>
>
>
>





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Re: [K2] ALC and power control on 40m SSB in K2/100

Don Wilhelm-4
In reply to this post by VK7JB
  John,

Is this a relatively new KPA100, or did you purchase an older kit from
someone who never built it?

The reason I ask is because the older T/R switch design had elements
that could cause parasitic oscillations near 40 meters, and often was
most noticeable on SSB.

If your KPA100 has blue toroid cores for L16 and RFC1, then it is the
new design.

If you have the new design, then did you fasten the shield directly to
the SO-239 jack using the two solder lugs as instructed?  These are
important.

Make a check - remove the KPA100 from the base K2, but keep it connected
- in other words turn the KPA100 upside-down on a book or box to the
right of the K2.  Then try your SSB operation again (into a dummy load
please, antennas are not consistent).  If it works OK with the KPA100
upside-down, then look for causes of coupling from the KPA100 into the
base K2, but if it still mis-behaves, we can look at other things.

73,
Don W3FPR

On 11/8/2010 6:15 PM, VK7JB wrote:

> Hello again folks,
>
> Sorry about the barrage of posts from me. Just playing with my K2/100 #6998.
>
> I've noticed that when operating in SSB  on 40m, requesting any power 15-20
> W and up will always give me 100W+ output, measured into a dummy load.
> Voice peaks are higher and result in Hi Curr warnings occasionally.  I can
> reduce the power above this threshold only by changing SSBC to 1:1 (normally
> run at 2:1 with my MH-2 mic) and winding the power out back to just on 11 W.
>
> CW and TUNE modes - all OK:  power requested and power output track very
> well on all bands, including 40m.
>
> Bands above 40m on SSB are not affected -  I mostly work 20m SSB and haven't
> noticed the power tracking issue there.  ALC seems to control the power out
> well there.
>
> I suspect the Tx chain gain on 40m is too high for the ALC to manage when in
> SSB.
>
> Is there any way of making the ALC more aggressive on 40m SSB, without
> affecting the other bands too much?  I remember seeing a previous post about
> this somewhere but haven't been able to find the details again.
>
> Any suggestions?
>
> 73,
>
> John
> VK7JB
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Re: [K2] ALC and power control on 40m SSB in K2/100

VK7JB
Don,

The KPA100 is new -from Elecraft in September 2010 - and it therefore is the new
design with the blue toroids @L16/RFC1.  The shield is installed as instructed,
using the 2 solder lugs to the SO-239 socket.

I took the KPA100 off the top of the rig, as you suggested, but there is no
difference in SSB mode running into the dummy load with the KPA100 attached or
flipped off beside the K2.

Looking more systematically, I see the overdrive is most noticable on 40m, but
is also  present on 80 and 30m.  It's not a problem on 20m and up.  Reducing
requested power to 50W (or less) and the power out remains close to 100W on
peaks and the ALC indicator shows 6-7+ bars in ALC mode. Seems the ALC is
working hard but not reducing the drive sufficiently to maintain the requested
output??

Mic is the MH-2 which I run SSBA = 1,  SSBC = 2. The audio sounds very good.
The problem reduces on the low bands with the compression setting @1:1, but then
there is insufficient drive  for 20m and up.  

Does this mean my TX chain has a lot of gain on 80/40/30 - too much for the ALC
to manage?

Thanks for your help,

John
VK7JB





Quoting Don Wilhelm <[hidden email]>:

>   John,
>
> Is this a relatively new KPA100, or did you purchase an older kit from
> someone who never built it?
>
> The reason I ask is because the older T/R switch design had elements
> that could cause parasitic oscillations near 40 meters, and often was
> most noticeable on SSB.
>
> If your KPA100 has blue toroid cores for L16 and RFC1, then it is the
> new design.
>
> If you have the new design, then did you fasten the shield directly to
> the SO-239 jack using the two solder lugs as instructed?  These are
> important.
>
> Make a check - remove the KPA100 from the base K2, but keep it connected
> - in other words turn the KPA100 upside-down on a book or box to the
> right of the K2.  Then try your SSB operation again (into a dummy load
> please, antennas are not consistent).  If it works OK with the KPA100
> upside-down, then look for causes of coupling from the KPA100 into the
> base K2, but if it still mis-behaves, we can look at other things.
>
> 73,
> Don W3FPR
>






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Re: [K2] ALC and power control on 40m SSB in K2/100

Don Wilhelm-4
  John,

At this point, check the audio drive and the SSBA menu parameter - which
should be at 1 for the MH2 (or other electret microphone).  SSBA = 2 and
SSBA = 3 are both the same and are normally not used with these microphones.

If you have any audio preamplifier installed, remove it for use with
that microphone, they have sufficient audio.

Before drawing conclusions, set the K2 to 20 meters and see how may ALC
bars are produced.  Check 10 meters too.  1 to 2 bars is sufficient for
the K2.
If you obtain more ALC bars than 1 or 2 on 10 meters, then you have too
much audio into the KSB2 board.

But if the audio drive is OK on those higher frequency bands (where the
RF Gain is lower), you will want to check (and possibly modify) the ALC
on the KSB2 board.

Assuming you have more than enough ALC bars on 20 through 10 meters,
make one more check - with SSBA set to 1, check the voltage at KSB2 U1
pin 10 (it should be near zero), and check the value and soldering of
KSB2 R14 and R15.

Then check the soldering of KSB2 D2, R9 (10k), Q1, R4 (56k) and C38.

If all the above is correct and the overdrive condition persists, then
change R9 to 15k (yes, I saw mention of 1.5k in this thread, but that is
incorrect), and cut the trace on the top of the board between P1 pin 6
and the base of Q1 and add a 1k resistor across the cut.  That should
tame things.  You can also pat yourself on the back, pleased that your
K2 RF chain has more gain than usual - due not only to component
tolerances, but also due to care during construction.

73,
Don W3FPR

On 11/9/2010 4:42 AM, [hidden email] wrote:

> Don,
>
> The KPA100 is new -from Elecraft in September 2010 - and it therefore is the new
> design with the blue toroids @L16/RFC1.  The shield is installed as instructed,
> using the 2 solder lugs to the SO-239 socket.
>
> I took the KPA100 off the top of the rig, as you suggested, but there is no
> difference in SSB mode running into the dummy load with the KPA100 attached or
> flipped off beside the K2.
>
> Looking more systematically, I see the overdrive is most noticable on 40m, but
> is also  present on 80 and 30m.  It's not a problem on 20m and up.  Reducing
> requested power to 50W (or less) and the power out remains close to 100W on
> peaks and the ALC indicator shows 6-7+ bars in ALC mode. Seems the ALC is
> working hard but not reducing the drive sufficiently to maintain the requested
> output??
>
> Mic is the MH-2 which I run SSBA = 1,  SSBC = 2. The audio sounds very good.
> The problem reduces on the low bands with the compression setting @1:1, but then
> there is insufficient drive  for 20m and up.
>
> Does this mean my TX chain has a lot of gain on 80/40/30 - too much for the ALC
> to manage?
>
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Re: [K2] ALC and power control on 40m SSB in K2/100

VK7JB
In reply to this post by VK7JB
Hello Group,

Just to complete the loop and to say thanks to Don, Steve and others who contributed to this discussion.

I've applied the mod to the KSB2 board - 1k0 resistor in series with the base of Q1 and changing the value of R9.  The ALC's can now control the output power of my K2 on 80/40/30m on SSB.

I'm very happy.  Thanks to everyone for your advice.

73,

John
VK7JB
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