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

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

Brian - N5BCN
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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Re: K2 - Unstable power output on 40m (digital modes)

GM4JJJ
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 <[hidden email]> 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: K2 - Unstable power output on 40m (digital modes)

GM4JJJ
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 <[hidden email]> 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 <[hidden email]> 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: K2 - Unstable power output on 40m (digital modes)

Don Wilhelm-4
In reply to this post by Brian - N5BCN
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: K2 - Unstable power output on 40m (digital modes)

Brian - N5BCN
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: K2 - Unstable power output on 40m (digital modes)

Don Wilhelm-4
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
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Unstable-power-output-on-40m-digital-modes-tp7609533p7609539.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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>

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

Bob McGraw - K4TAX
In reply to this post by Brian - N5BCN
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: K2 - Unstable power output on 40m (digital modes)

k6dgw
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: K2 - Unstable power output on 40m (digital modes)

Jim Brown-10
In reply to this post by Bob McGraw - K4TAX
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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Re: OT on balun usage

Bob McGraw - K4TAX
In reply to this post by k6dgw
One point I've learned over the years is the fact baluns, regardless of
the ratio, are power rated at matched values.  i.e. a 1:1 is typically a
50 ohm to 50 ohm while a 4:1 is nominally a 200 ohm to 50 ohm device.  
And the power rating is mostly at closely matched values.  Hence a 4:1
balun is good for feeding a 1/2 wave folded dipole which, at nominal
height above ground, is about 200 to 300 ohms where as a 1:1 balun is
good for a 1/2 wave dipole at near resonant frequency.

Therefore a 4:1 balun may be good for say 1KW if the Z's are correct.  
Try to use one on a complex reactive load and the 1KW rating fails
rather quickly.  For that reason, for any balun I use and choose, it  is
rated at 5x to 10x the expected power.  Thus a 1KW balun is good for
about 100 watts.    I recently "smoked badly" a 4:1 known brand 5KW
balun on 160M with my AM transmitter at legal limit when I connected the
80M folded dipole antenna in error Shouldn't have done that.   The
transmitter didn't care but lots of smoke came out of the balun box.

73
Bob, K4TAX

On 10/25/2015 2:57 PM, Fred Jensen wrote:
> 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.


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Re: OT on balun usage

Barry K3NDM
Bob,
     You are quite correct, and your recommendation to use a balun rated
at higher power levels than you plan to run is dead on. One point; in
the main, it is better to use a current type rather than a voltage
balun. Between your recommendation and my suggestion, a number of
problems get addressed and need not be of bother to the average ham.


73,
Barry
K3NDM

------ Original Message ------
From: "Bob McGraw - K4TAX" <[hidden email]>
To: [hidden email]
Sent: 10/25/2015 8:41:06 PM
Subject: Re: [Elecraft] OT on balun usage

>One point I've learned over the years is the fact baluns, regardless of
>the ratio, are power rated at matched values.  i.e. a 1:1 is typically
>a 50 ohm to 50 ohm while a 4:1 is nominally a 200 ohm to 50 ohm device.
>  And the power rating is mostly at closely matched values.  Hence a 4:1
>balun is good for feeding a 1/2 wave folded dipole which, at nominal
>height above ground, is about 200 to 300 ohms where as a 1:1 balun is
>good for a 1/2 wave dipole at near resonant frequency.
>
>Therefore a 4:1 balun may be good for say 1KW if the Z's are correct.  
>Try to use one on a complex reactive load and the 1KW rating fails
>rather quickly.  For that reason, for any balun I use and choose, it  
>is rated at 5x to 10x the expected power.  Thus a 1KW balun is good for
>about 100 watts.    I recently "smoked badly" a 4:1 known brand 5KW
>balun on 160M with my AM transmitter at legal limit when I connected
>the 80M folded dipole antenna in error Shouldn't have done that.   The
>transmitter didn't care but lots of smoke came out of the balun box.
>
>73
>Bob, K4TAX
>
>On 10/25/2015 2:57 PM, Fred Jensen wrote:
>>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.
>
>
>______________________________________________________________
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>
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