Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Don Wilhelm]

Brian,

Do things settle down if you drive a dummy load instead of the antenna?  
If so, that would nail it as an RF Feedback.  If that is the case, use a 
good quality common mode choke at the junction of the coax with the 
ladderline.  See K9YC's RFI information at 
http://audiosystemsgroup.com/RFI-Ham.pdf - chapters 6 and 7 cover making 
effective feedline chokes.


Also investigate your KPA100 to see if it has the latest upgrade. The 
T/R switch was changed to eliminate instability on 40 meters.
Remove the right side panel of the K2 and peer between the KPA100 shield 
and board.  If you see blue toroid cores at RFC1 and L16, you have the 
updated version.  If you see red cores, update with KPA100UPKT.
You may also have to update the shield.  If you do not have shield clips 
to connect the shield to the sides of the base K2 and a shield over the 
speaker magnet, add the KPA100SHLDKT.


73,
Don W3FPR


On 10/25/2015 1:45 AM, Brian - N5BCN via Elecraft wrote:

I'm having an issue with unstable power output using digital modes on 40m
above about 20 watts.  All other bands seem to be ok.

My antenna setup is as follows: a loop consisting of about 245 feet of wire,
feed line consists of about 21 feet of 450 ohm ladderline to an Elecraft BL2
balun, then about 3 feet of coax to KAT100/KPA100/K2.  I've tried the balun
in 1:1 and 4:1 configs with no apparent change.  The feed point of the loop
is in the attic above the shack, but the majority of the wire is outside
running along a wood fence.

No problems tuning any band including 40m.  When using digital modes, power
output and ALC action (no bars) appears normal on 10 through 30m, and even
works ok on 80m.  Haven't tried 160m.




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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[David Anderson]

Brian,

The Elecraft K series requires a different way of setting power out on digital. 

You increase the audio drive from the SignaLink until the "ALC" meter is 
showing 4 to 5 bars and then adjust the power control to set the required power 
out, do not use the audio level to adjust the power.

The "ALC" meter is actually just an audio level meter until the 6th bar when 
actual power reducing ALC starts. 

I know this apparently goes against normal advice to not have any ALC showing, 
but in effect you are not because of the way the "ALC" meter on the K series is 
configured. There is no ALC action until the 6th bar of "ALC".

If you don't have sufficient audio (4 to 5 bars of "ALC" ) then the radio power 
output will be unstable as you have described.


73

David Anderson GM4JJJ 

> On 25 Oct 2015, at 05:45, Brian - N5BCN via Elecraft 
>  wrote:
> 
> No problems tuning any band including 40m.  When using digital modes, power
> output and ALC action (no bars) appears normal on 10 through 30m, and even
> works ok on 80m.  Haven't tried 160m.
> 
> However, when attempting digital modes (using a Signalink) on 40m, power
> output and ALC action is "all over the place" and generally folds back to a
> couple of watts.  The output also seems to be extremely "touchy" and
> sensitive to the TX drive setting on the Signalink that's not apparent on
> other bands.  I don't see this craziness using a dummy load, so I'm
> suspecting maybe I'm getting RF feedback only on 40m for some reason.
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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[David Anderson]

Brian,

Too early in the morning with me, I just noticed the fact you have a K2 not a 
K3 or KX3.

In that case the ALC meter is different, but perhaps you may find something 
that is helpful on the late G4ILO's site:

http://www.g4ilo.com/k2psk31.html


73

David Anderson GM4JJJ 

> On 25 Oct 2015, at 09:19, David Anderson  wrote:
> 
> Brian,
> 
> The Elecraft K series requires a different way of setting power out on 
> digital. 
> 
> Snip..


> 
>> On 25 Oct 2015, at 05:45, Brian - N5BCN via Elecraft 
>>  wrote:
>> 
>> No problems tuning any band including 40m.  When using digital modes, power
>> output and ALC action (no bars) appears normal on 10 through 30m, and even
>> works ok on 80m.  Haven't tried 160m.
>> 
>> How
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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Brian - N5BCN via Elecraft]

Don,

Yes, things settle down with a dummy load, so it looks like I'm dealing with
RF feedback.

Per the original post, I'm using an Elecraft BL2 balun at the
coax/ladderline junction.  Shouldn't this act as the common mode choke that
you suggest or are you suggesting to place a common mode choke in addition
to the balun?

Interesting idea regarding the KPA100 latest version since 40m is the
troublesome band.  I purchased the KPA100 around 2011-2012, so I would think
it has the latest hardware but I'll double check when I get a chance.

73 Brian, N5BCN



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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Bob McGraw - K4TAX]

My take on this is baluns are baluns and common mode chokes are common 
mode chokes.  In many cases baluns do not provide adequate common mode 
choking requirements.  Thus both may be needed. Usually, the balun is 
located physically at the load and the common mode choke is located at 
the source.In certain antenna configurations, a balun is used at the 
feed point along with a common mode choke and then a 2nd common mode 
choke at the source is required as well.


73
Bob, K4TAX
K3S s/n 10163
 


On 10/25/2015 10:09 AM, Brian - N5BCN via Elecraft wrote:

Don,

Yes, things settle down with a dummy load, so it looks like I'm dealing with
RF feedback.

Per the original post, I'm using an Elecraft BL2 balun at the
coax/ladderline junction.  Shouldn't this act as the common mode choke that
you suggest or are you suggesting to place a common mode choke in addition
to the balun?

Interesting idea regarding the KPA100 latest version since 40m is the
troublesome band.  I purchased the KPA100 around 2011-2012, so I would think
it has the latest hardware but I'll double check when I get a chance.

73 Brian, N5BCN



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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Fred Jensen]

Yep, almost.  The word "balun" is a portmanteau of "balanced" and 
"unbalanced."  They are transformers or auto-transformers and their job 
is to keep a balanced feed to the antenna balanced when transitioning to 
unbalanced coax.  Since they're transformers, they can also transform 
the impedance.


Common mode chokes act as a series high impedance to current on the 
outside of the coax shield.  For RF, coaxial cable is really a 
3-conductor circuit because of the so-called "skin effect" ... inner 
conductor and inside of shield form one path are is unaffected by a CM 
choke.  Current can also be induced on the outside of the shield and is 
the common-mode current.  When transmitting, they can radiate close to 
the shack and get into places that don't like RF.  They can also distort 
the radiation pattern of the antenna.  When receiving, the outside of 
the shield acts as a vertical antenna and can pick up noise.


CM chokes are often a string of ferrite toroids taped together with the 
coax going through them.  Sometimes, the coax is wound several times 
through a larger toroid.  First place to put them is at the antenna-end 
of the coax.  In some cases, a CM choke at the station entrance will 
help as well, but it's not the first choice.


Jim, K9YC, has prepared "Common Mode Chokes [and other things] For 
Dummies" at http://audiosystemsgroup.com/RFI-Ham.pdf  It's full of 
information, including some charts demonstrating that all ferrites are 
not created equal.


73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org


On 10/25/2015 12:32 PM, Bob McGraw - K4TAX wrote:

My take on this is baluns are baluns and common mode chokes are common
mode chokes.  In many cases baluns do not provide adequate common mode
choking requirements.  Thus both may be needed. Usually, the balun is
located physically at the load and the common mode choke is located at
the source.In certain antenna configurations, a balun is used at the
feed point along with a common mode choke and then a 2nd common mode
choke at the source is required as well.


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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Don Wilhelm]

Brian,

The Elecraft BL2 is a good common mode choke.  It is rated at 250 watts 
into a *matched* load.
Your load certainly is not matched, and I do not know how to de-rate the 
power for any given load.
Check to see if the balun core heats - if so, you could be operating the 
BL2 outside its range of capability.

Note that I am only making a guess here.

One thing that you could do is to remove the coax from the tuner and 
measure the impedance of the entire antenna system with an antenna 
analyzer.  That will give you a better idea of whether to use the 1:1 or 
4:1 position on the balun.


Another thing to consider is the position on the antenna feedline in 
relationship to the radiator - the feedline should come away from the 
radiator at right angles for as far as possible.  If it does not, energy 
from the radiator can couple onto the feedline and create common mode 
current that is difficult to choke off - in that case, the choking 
impedance of the BL2 may not be sufficient and you may have to add 
additional common mode chokes.


As a quick test for common mode current on 40 meters, yes try tying a 33 
foot counterpoise wire to the ground post on the BL2 - keep the far end 
isolated and insulated because it will have a high RF voltage on it.  If 
it makes a difference, then you will have to get rid of the common mode 
current on the feedline.


73,
Don W3FPR

On 10/25/2015 11:09 AM, Brian - N5BCN via Elecraft wrote:

Don,

Yes, things settle down with a dummy load, so it looks like I'm dealing with
RF feedback.

Per the original post, I'm using an Elecraft BL2 balun at the
coax/ladderline junction.  Shouldn't this act as the common mode choke that
you suggest or are you suggesting to place a common mode choke in addition
to the balun?

Interesting idea regarding the KPA100 latest version since 40m is the
troublesome band.  I purchased the KPA100 around 2011-2012, so I would think
it has the latest hardware but I'll double check when I get a chance.

73 Brian, N5BCN



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Re: [Elecraft] K2 - Unstable power output on 40m (digital modes)

[Jim Brown]

Yes. And even more important -- the word "balun" is used to describe so 
many (at least) ten different very kinds of components that the word 
itself should be banned from our language.  ONE of those components is a 
common mode choke. Another is an array of common mode chokes. Another is 
a simple transformer. Another is a simple autotransformer. Another is a 
section of transmission line. Another is an array of sections of 
transmission line. Another is an active device to put broadband video on 
twisted pair. And so on.


73, Jim K9YC

On Sun,10/25/2015 12:32 PM, Bob McGraw - K4TAX wrote:
My take on this is baluns are baluns and common mode chokes are common 
mode chokes.  In many cases baluns do not provide adequate common mode 
choking requirements.  Thus both may be needed. Usually, the balun is 
located physically at the load and the common mode choke is located at 
the source.In certain antenna configurations, a balun is used at 
the feed point along with a common mode choke and then a 2nd common 
mode choke at the source is required as well.


73 


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[Elecraft] K2 - Unstable power output on 40m (digital modes)

[Brian - N5BCN via Elecraft]

I'm having an issue with unstable power output using digital modes on 40m
above about 20 watts.  All other bands seem to be ok.

My antenna setup is as follows: a loop consisting of about 245 feet of wire,
feed line consists of about 21 feet of 450 ohm ladderline to an Elecraft BL2
balun, then about 3 feet of coax to KAT100/KPA100/K2.  I've tried the balun
in 1:1 and 4:1 configs with no apparent change.  The feed point of the loop
is in the attic above the shack, but the majority of the wire is outside
running along a wood fence.

No problems tuning any band including 40m.  When using digital modes, power
output and ALC action (no bars) appears normal on 10 through 30m, and even
works ok on 80m.  Haven't tried 160m.

However, when attempting digital modes (using a Signalink) on 40m, power
output and ALC action is "all over the place" and generally folds back to a
couple of watts.  The output also seems to be extremely "touchy" and
sensitive to the TX drive setting on the Signalink that's not apparent on
other bands.  I don't see this craziness using a dummy load, so I'm
suspecting maybe I'm getting RF feedback only on 40m for some reason.

I'm not sure what to try to mitigate this.  The variables I could change
would be to increase/decrease the ladderline length, try a more robust
balun, or maybe try a counterpoise wire tied to the balun's ground lug?  Any
ideas and suggestions would be most appreciated, I sure would like to be
able to use 40m!

73 Brian, N5BCN



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