Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[Eric Swartz]

Folks - Thread CLOSED. In the interest of relieving mail overload for those
who are not interested in the argument on this topic, please take this off
the list as it has been beaten to death.

73,
Eric
List moderator, COO, CFO and general playground monitor.. ;-)

*elecraft.com *


On Fri, Nov 5, 2021 at 11:13 AM Jim Brown  wrote:

> On 11/5/2021 4:24 AM, CUTTER DAVID via Elecraft wrote:
> > As has been said on many occasions, there is no real difference between
> a dipole fed in the middle and one fed off centre: as long as you can get
> the current to run in the dipole by suitable matching and don't waste it
> along the way, they are indistinguishable to the dx station.
>
> Statements like this ignore three fundamental facts.
>
> 1) Off-center fed antennas are noisy on receive, and you can't work who
> you can't hear. This usually doesn't matter in the middle of nowhere,
> but it matters a LOT in most of the developed world, where all of us are
> surrounded by switch-mode power supplies (almost everything that plugs
> into the wall), controllers for variable speed motors (HVAC systems and
> other systems), grow lights, and solar systems.
>
> 2) When used on bands other than their half-wave length, horizontal
> patterns are wildly variable, with multiple peaks and nulls at angles
> predictable by antenna fundamentals.
>
> 3) It is impractical to EFFECTIVELY choke them at the feedpoint to kill
> RX noise, the feedpoint being at the off-center point on the horizontal
> wire, not down the matching section from the antenna, and it is also
> impractical to EFFECTIVELY choke a feedline where it is severely
> mismatched. Again, this doesn't matter in the middle of nowhere, but it
> matters a LOT where most of us live.
>
> And it DOES matter to the DX station who calls you repeatedly and you
> don't hear him, thanks to your RX noise. This has been happening to me a
> lot on 60M FT8, where I'm licensed for 100W EIRP, and most of the rest
> of the world is licensed for 15-25W. That power gives me a 6-8 dB
> advantage, and stations I decode at -10 dB don't hear me!
>
> 73, Jim K9YC
>
> 73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[Jim Brown]

On 11/5/2021 4:24 AM, CUTTER DAVID via Elecraft wrote:

As has been said on many occasions, there is no real difference between a 
dipole fed in the middle and one fed off centre: as long as you can get the 
current to run in the dipole by suitable matching and don't waste it along the 
way, they are indistinguishable to the dx station.


Statements like this ignore three fundamental facts.

1) Off-center fed antennas are noisy on receive, and you can't work who 
you can't hear. This usually doesn't matter in the middle of nowhere, 
but it matters a LOT in most of the developed world, where all of us are 
surrounded by switch-mode power supplies (almost everything that plugs 
into the wall), controllers for variable speed motors (HVAC systems and 
other systems), grow lights, and solar systems.


2) When used on bands other than their half-wave length, horizontal 
patterns are wildly variable, with multiple peaks and nulls at angles 
predictable by antenna fundamentals.


3) It is impractical to EFFECTIVELY choke them at the feedpoint to kill 
RX noise, the feedpoint being at the off-center point on the horizontal 
wire, not down the matching section from the antenna, and it is also 
impractical to EFFECTIVELY choke a feedline where it is severely 
mismatched. Again, this doesn't matter in the middle of nowhere, but it 
matters a LOT where most of us live.


And it DOES matter to the DX station who calls you repeatedly and you 
don't hear him, thanks to your RX noise. This has been happening to me a 
lot on 60M FT8, where I'm licensed for 100W EIRP, and most of the rest 
of the world is licensed for 15-25W. That power gives me a 6-8 dB 
advantage, and stations I decode at -10 dB don't hear me!


73, Jim K9YC

73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[Ray]

Great Article…….
WA6VAB  Ray  K3 

Sent from Mail for Windows

From: CUTTER DAVID via Elecraft
Sent: Friday, November 5, 2021 4:24 AM
To: k...@altaeng.com; elecraft@mailman.qth.net
Subject: Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

Chuck

I'm not an expert but you might find it useful to read
http://www.karinya.net/g3txq/baluns/baluns.pdf

Antennas popular with Elecraft back-packers are off centre fed dipoles: eg 20ft 
of wire up a tree and 10ft of wire on the ground as an example.
Many low power and one-man dxpeditions use these antennas and win trophies!  
I used an 80m ocf dipole in an IOTA contest with team CR5CW running 100W and a 
K3 and did pretty well. 

As has been said on many occasions, there is no real difference between a 
dipole fed in the middle and one fed off centre: as long as you can get the 
current to run in the dipole by suitable matching and don't waste it along the 
way, they are indistinguishable to the dx station.  Centre fed multi-band 
antennas can waste power in the matching unit, take care. Use Elecraft internal 
matching and it's all plug and play. 

Build one or buy one and just have multi-band fun from one antenna.  

David G3UNA


> On 04 November 2021 at 20:54 Charles K0MV  wrote:
> 
> 
> Hi David,
> 
> Thanks for the synopsis below.  I found it very useful being unfamiliar 
> with amateur practice over the years with OCF antennas.  My antennas are 
> all center fed.
> 
> I replied to this message because it was the most informative. Other, 
> later messages on this thread were also interesting.  But generally, the 
> discussion lacks quantitative data and so it is difficult to objectively 
> evaluate the efficacy and drawbacks of different realizations.  It is 
> also difficult to project which realization or changes would fit a given 
> set of constraints.
> 
> The positive aspect is there has been years and years of experimentation 
> and different approaches to this multiband dipole problem.  I would like 
> to hear more on these.
> 
> Could you describe G3TXQ's 2 core Guanella balun solution more 
> completely?  I checked the Spiderbeam website and it is not clear to me.
> 
> I think this is relevant to Elecraft since many applications are 
> portable and QRP.  We want that antenna to really work and understanding 
> it better, helps.
> 
> 73,
> 
> Chuck K0MV
> 
> 
> On 11/4/21 9:59 AM, CUTTER DAVID via Elecraft wrote:
> > Hi Dan
> >
> > Good question.  I'll answer as a non-expert as best I can.
> >
> > This is essentially a quest for a multi-band dipole that is easy to make 
> > and use.  If you can put up mono band dipoles and beams for all your bands, 
> > you probably will not bother going this route.
> >
> > The popular description of the ocf dipole (going back at least to the 50's) 
> > has a feed point of one third/two thirds on the dipole.  (BTW this is 
> > otherwise a normal half wavelength dipole.
> >
> > This provides approximately 200 ohm feed point impedance for most popular 
> > HF bands, eg 80, 40, 20 and 10m, not 15m.
> >
> > Back in the 60's we could use coax into a valve PA, which I preferred to 
> > the G5RV which needed an outboard matching unit.  In transistor days we 
> > used a modest matching unit with an swr meter and were ignorant of common 
> > mode current.
> >   
> > In the 90s I used ladder line to ground level and an auto-tuning unit into 
> > a tent for field day, believing it to be more efficient.   With grounded 
> > coax I didn't have live chassis syndrome and out in the wilds there was no 
> > noise pickup.  Later I used ladder line through a balun then into the radio 
> > with an on-board matching unit and that was, for me a great step forward 
> > with auto-tuning.
> >
> >
> > It was discovered by some users that the common mode current performance 
> > using off-the-shelf baluns and chokes was inadequate and could result in 
> > live chassis syndrome and noise pickup on receive from home locations.  
> > Poor matching on 15m was still a problem as were the WARC bands.
> >
> > Now in the 21st Century, just a few years ago, Rick DJ0IP tackled the 
> > problem starting with a 40m ocf dipole using a new balun/choke combination. 
> >  He read that W8JI and others recommended a 20% feedpoint to bring 15m into 
> > the 200 ohm region. He then used a Guanella 2-core balun solution from 
> > Steve G3TXQ and others to provide the 50 ohm output with low common mode 
> > current.  It had to be the dual core version, the single core version 
> > simply didn't suppress the cmc.  This is now marketed by Spiderbeam.  
> > Moving to an 80m version was difficult but with a hybrid balun/c

Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[CUTTER DAVID via Elecraft]

Chuck

I'm not an expert but you might find it useful to read
http://www.karinya.net/g3txq/baluns/baluns.pdf

Antennas popular with Elecraft back-packers are off centre fed dipoles: eg 20ft 
of wire up a tree and 10ft of wire on the ground as an example.
Many low power and one-man dxpeditions use these antennas and win trophies!  
I used an 80m ocf dipole in an IOTA contest with team CR5CW running 100W and a 
K3 and did pretty well. 

As has been said on many occasions, there is no real difference between a 
dipole fed in the middle and one fed off centre: as long as you can get the 
current to run in the dipole by suitable matching and don't waste it along the 
way, they are indistinguishable to the dx station.  Centre fed multi-band 
antennas can waste power in the matching unit, take care. Use Elecraft internal 
matching and it's all plug and play. 

Build one or buy one and just have multi-band fun from one antenna.  

David G3UNA


> On 04 November 2021 at 20:54 Charles K0MV  wrote:
> 
> 
> Hi David,
> 
> Thanks for the synopsis below.  I found it very useful being unfamiliar 
> with amateur practice over the years with OCF antennas.  My antennas are 
> all center fed.
> 
> I replied to this message because it was the most informative. Other, 
> later messages on this thread were also interesting.  But generally, the 
> discussion lacks quantitative data and so it is difficult to objectively 
> evaluate the efficacy and drawbacks of different realizations.  It is 
> also difficult to project which realization or changes would fit a given 
> set of constraints.
> 
> The positive aspect is there has been years and years of experimentation 
> and different approaches to this multiband dipole problem.  I would like 
> to hear more on these.
> 
> Could you describe G3TXQ's 2 core Guanella balun solution more 
> completely?  I checked the Spiderbeam website and it is not clear to me.
> 
> I think this is relevant to Elecraft since many applications are 
> portable and QRP.  We want that antenna to really work and understanding 
> it better, helps.
> 
> 73,
> 
> Chuck K0MV
> 
> 
> On 11/4/21 9:59 AM, CUTTER DAVID via Elecraft wrote:
> > Hi Dan
> >
> > Good question.  I'll answer as a non-expert as best I can.
> >
> > This is essentially a quest for a multi-band dipole that is easy to make 
> > and use.  If you can put up mono band dipoles and beams for all your bands, 
> > you probably will not bother going this route.
> >
> > The popular description of the ocf dipole (going back at least to the 50's) 
> > has a feed point of one third/two thirds on the dipole.  (BTW this is 
> > otherwise a normal half wavelength dipole.
> >
> > This provides approximately 200 ohm feed point impedance for most popular 
> > HF bands, eg 80, 40, 20 and 10m, not 15m.
> >
> > Back in the 60's we could use coax into a valve PA, which I preferred to 
> > the G5RV which needed an outboard matching unit.  In transistor days we 
> > used a modest matching unit with an swr meter and were ignorant of common 
> > mode current.
> >   
> > In the 90s I used ladder line to ground level and an auto-tuning unit into 
> > a tent for field day, believing it to be more efficient.   With grounded 
> > coax I didn't have live chassis syndrome and out in the wilds there was no 
> > noise pickup.  Later I used ladder line through a balun then into the radio 
> > with an on-board matching unit and that was, for me a great step forward 
> > with auto-tuning.
> >
> >
> > It was discovered by some users that the common mode current performance 
> > using off-the-shelf baluns and chokes was inadequate and could result in 
> > live chassis syndrome and noise pickup on receive from home locations.  
> > Poor matching on 15m was still a problem as were the WARC bands.
> >
> > Now in the 21st Century, just a few years ago, Rick DJ0IP tackled the 
> > problem starting with a 40m ocf dipole using a new balun/choke combination. 
> >  He read that W8JI and others recommended a 20% feedpoint to bring 15m into 
> > the 200 ohm region. He then used a Guanella 2-core balun solution from 
> > Steve G3TXQ and others to provide the 50 ohm output with low common mode 
> > current.  It had to be the dual core version, the single core version 
> > simply didn't suppress the cmc.  This is now marketed by Spiderbeam.  
> > Moving to an 80m version was difficult but with a hybrid balun/choke 
> > combination he devised a combination that provided at least as good cmc and 
> > this version is also marketed by Spiderbeam. They both work on 15m and some 
> > WARC bands. For some layouts a modest on-board matching unit is required 
> > for complete coverage which is a far cry from bulky outboard units; good 
> > news for portable operation.
> >
> > I would call these *modern* off centre-fed dipoles, ie well into this 
> > century.
> >
> > I have no financial connection with anyone in that business and I will say 
> > that I have never seen anyone else produce such a large 

Re: [Elecraft] Problem Tuning K3

[JR]

Comparison with a real dipole...

--

My local expert (and the ARRL Handbooks) and others, including I believe 
Joel Hallas of the ARRL,  all say an OCF Dipole  IS A DIPOLE and 
radiates just like a center fed dipole, but with a different feed point 
impedance ,  which is resolved with a matching unit (choke and balun. ) 
   Where is your proof the OCF radiates differently?   If different, it 
won't matter enough to make it a poor choice.   Nonsense.   K8JHR

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Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[Charles K0MV]

Hi David,

Thanks for the synopsis below.  I found it very useful being unfamiliar 
with amateur practice over the years with OCF antennas.  My antennas are 
all center fed.


I replied to this message because it was the most informative. Other, 
later messages on this thread were also interesting.  But generally, the 
discussion lacks quantitative data and so it is difficult to objectively 
evaluate the efficacy and drawbacks of different realizations.  It is 
also difficult to project which realization or changes would fit a given 
set of constraints.


The positive aspect is there has been years and years of experimentation 
and different approaches to this multiband dipole problem.  I would like 
to hear more on these.


Could you describe G3TXQ's 2 core Guanella balun solution more 
completely?  I checked the Spiderbeam website and it is not clear to me.


I think this is relevant to Elecraft since many applications are 
portable and QRP.  We want that antenna to really work and understanding 
it better, helps.


73,

Chuck K0MV


On 11/4/21 9:59 AM, CUTTER DAVID via Elecraft wrote:

Hi Dan

Good question.  I'll answer as a non-expert as best I can.

This is essentially a quest for a multi-band dipole that is easy to make and 
use.  If you can put up mono band dipoles and beams for all your bands, you 
probably will not bother going this route.

The popular description of the ocf dipole (going back at least to the 50's) has 
a feed point of one third/two thirds on the dipole.  (BTW this is otherwise a 
normal half wavelength dipole.

This provides approximately 200 ohm feed point impedance for most popular HF 
bands, eg 80, 40, 20 and 10m, not 15m.

Back in the 60's we could use coax into a valve PA, which I preferred to the 
G5RV which needed an outboard matching unit.  In transistor days we used a 
modest matching unit with an swr meter and were ignorant of common mode current.
  
In the 90s I used ladder line to ground level and an auto-tuning unit into a tent for field day, believing it to be more efficient.   With grounded coax I didn't have live chassis syndrome and out in the wilds there was no noise pickup.  Later I used ladder line through a balun then into the radio with an on-board matching unit and that was, for me a great step forward with auto-tuning.



It was discovered by some users that the common mode current performance using 
off-the-shelf baluns and chokes was inadequate and could result in live chassis 
syndrome and noise pickup on receive from home locations.  Poor matching on 15m 
was still a problem as were the WARC bands.

Now in the 21st Century, just a few years ago, Rick DJ0IP tackled the problem 
starting with a 40m ocf dipole using a new balun/choke combination.  He read 
that W8JI and others recommended a 20% feedpoint to bring 15m into the 200 ohm 
region. He then used a Guanella 2-core balun solution from Steve G3TXQ and 
others to provide the 50 ohm output with low common mode current.  It had to be 
the dual core version, the single core version simply didn't suppress the cmc.  
This is now marketed by Spiderbeam.  Moving to an 80m version was difficult but 
with a hybrid balun/choke combination he devised a combination that provided at 
least as good cmc and this version is also marketed by Spiderbeam. They both 
work on 15m and some WARC bands. For some layouts a modest on-board matching 
unit is required for complete coverage which is a far cry from bulky outboard 
units; good news for portable operation.

I would call these *modern* off centre-fed dipoles, ie well into this century.

I have no financial connection with anyone in that business and I will say that 
I have never seen anyone else produce such a large amount of compelling 
evidence as Rick and I recommend his web site for all things balun and choke 
related to this task.  He takes the practical, non-laboratory approach.  This 
in no way conflicts with any work done by Jim, K9YC and I only wish that he 
would make his own measurements on these modern devices and let go the old 
prejudice.

73 David G3UNA
   
  






On 04 November 2021 at 05:24 Dan Presley  wrote:


Perhaps you could clarify what you meant by a modern OCF. What’s changed from 
the traditional model? Thanks.

Dan Presley 503-701-3871
danpresley@me. com
n7...@arrl.net


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--
Charles K0MV
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Re: [Elecraft] Problem Tuning K3

[Wes]

It should be noted that Jim is an opinionated, crotchety, 80-year old man.

I get a pass while saying this because I am also an opinionated, crotchety, 
80-year old man.


Wes  N7WS


On 11/4/2021 12:37 PM, Jim Brown wrote:

It should be noted that K8JHR is a lawyer, not an engineer or scientist.

73, Jim K9YC



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Re: [Elecraft] Problem Tuning K3

[Edward Mccann]

I wonder if this food fight might reach its denouement on another channel?

It seems to have been sparked by an OCFD discussion not relevant to anything 
Elecraft, and to have evolved into personal preferences and grievances. 

Maybe we should take on End Fed Zepps next?  Or take the whole thing off-line?

If it continues, we are indeed eminently qualified in the use of our delete 
buttons.

Best from the West,

Ed McCann
AG6CX

Sent from my iPhone

> On Nov 4, 2021, at 12:39 PM, Bill Lederer  wrote:
> 
> Not Dick Tracy here, nor am I K9YC.
> 
> I had very good results running mobile with 100 watts and a hustler on the
> roof of my Suburban. I also have fun with my kx2 and a random wire 15 feet
> high out the window to a tree.
> 
> Your notes about the success of various real-world examples leaves out what
> the comparison would be with a true dipole. For a true test, you would need
> to do a head-to-head comparison of the two antennas. K3LR used to do this
> at Dayton.  Proof is not how many OCF antennas fly above roofs, but how do
> they compare to a similarly situated dipole.
> 
> A true test of equipment and antennas is how well they do in a contest.
> With these OCF antennas, can you work 100 countries in a weekend on
> multiple bands? Can you get to 300 countries in DXCC? Much less likely than
> dipoles, properly built verticals or beams.
> 
> Can you have fun with OCF or other compromise antennas? Yes. But other
> antennas are likely to do better.
> 
> w8lvn
> 
> 
> 
> 
>> On Thu, Nov 4, 2021 at 12:00 PM JR  wrote:
>> 
>> Jim Brown says --
>> 
>>I suspect you don't understand the physics of
>>the problem. OCF antennas are a yesterday's approach
>>to multiband antennas. They are a recipe for RX noise
>>and RF in the shack.
>> 
>> ___
>> 
>> NOT SO, DICK TRACY !
>> 
>> While YOUR OCF dipole may have problems if poorly deployed and
>> implemented.  It is a PLAIN FACT based on thousands of real world examples,
>> OCF Dipoles DO WORK WELL.  Mine works very well with NO CMC or other
>> problems.  A few years ago, I gave some minor assistance to a notorious
>> German operator, DJ0IP, as he collected a wealth of empirical data on CMC
>> and OCF dipoles, carefully testing multiple examples before designing a
>> commercial product that has been well received by the QRP crowd, receiving
>> positive reviews in the RSGB and ARRL magazines.  He received even more
>> assistance from W8JI and G4TXQ and others,focusing their attention on how
>> to avoid common mode current (CMC),  discussing where to offset the feed
>> point, and how to construct a proper combination balun and choke.  My OCF
>> Dipole is split 25% /75% split and Rick selected a very different feed
>> point, and all is good.
>> 
>> CMC is NOT a necessary evil as Mr. Brown suggests. It CAN be curtailed
>> with "proper care and feeding" (pun intended) and the proof flies over my
>> shack, and over hundreds of other shacks, including DJ0IP's station, around
>> the globe.
>> 
>> Pedantic dogma be hanged !!  I base my claim on 1) real world results,
>> 2) TONS of empirical research by others,  and 3) input from my local
>> Elmer/guru who designed RF gear for NASA and the AIR FORCE and commercial
>> interests.  Mr. B's theory is out of step with the real world.(smiling
>> as he typed that, Pardner...)  :-)  -K8JHR-
>> 
>> __
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>> 
> 
> 
> -- 
> --w8lvn--
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Re: [Elecraft] Problem Tuning K3

[Jim Brown]

On 11/4/2021 12:38 PM, Bill Lederer wrote:

Can you have fun with OCF or other compromise antennas? Yes. But other
antennas are likely to do better.


Exactly right. On my Chicago city lot, I had a fan dipole for 20/15/10, 
a trap dipole for those bands, and an inductively loaded dipole for 80 
and 40 that also worked in some directions on 30, and that I used as 
top-loaded vertical on 80 and 160M, using a wrought iron fence as a 
counterpoise.


73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3

[Bill Lederer]

Not Dick Tracy here, nor am I K9YC.

I had very good results running mobile with 100 watts and a hustler on the
roof of my Suburban. I also have fun with my kx2 and a random wire 15 feet
high out the window to a tree.

Your notes about the success of various real-world examples leaves out what
the comparison would be with a true dipole. For a true test, you would need
to do a head-to-head comparison of the two antennas. K3LR used to do this
at Dayton.  Proof is not how many OCF antennas fly above roofs, but how do
they compare to a similarly situated dipole.

A true test of equipment and antennas is how well they do in a contest.
With these OCF antennas, can you work 100 countries in a weekend on
multiple bands? Can you get to 300 countries in DXCC? Much less likely than
dipoles, properly built verticals or beams.

Can you have fun with OCF or other compromise antennas? Yes. But other
antennas are likely to do better.

w8lvn




On Thu, Nov 4, 2021 at 12:00 PM JR  wrote:

> Jim Brown says --
>
> I suspect you don't understand the physics of
> the problem. OCF antennas are a yesterday's approach
> to multiband antennas. They are a recipe for RX noise
> and RF in the shack.
>
> ___
>
> NOT SO, DICK TRACY !
>
> While YOUR OCF dipole may have problems if poorly deployed and
> implemented.  It is a PLAIN FACT based on thousands of real world examples,
> OCF Dipoles DO WORK WELL.  Mine works very well with NO CMC or other
> problems.  A few years ago, I gave some minor assistance to a notorious
> German operator, DJ0IP, as he collected a wealth of empirical data on CMC
> and OCF dipoles, carefully testing multiple examples before designing a
> commercial product that has been well received by the QRP crowd, receiving
> positive reviews in the RSGB and ARRL magazines.  He received even more
> assistance from W8JI and G4TXQ and others,focusing their attention on how
> to avoid common mode current (CMC),  discussing where to offset the feed
> point, and how to construct a proper combination balun and choke.  My OCF
> Dipole is split 25% /75% split and Rick selected a very different feed
> point, and all is good.
>
> CMC is NOT a necessary evil as Mr. Brown suggests. It CAN be curtailed
> with "proper care and feeding" (pun intended) and the proof flies over my
> shack, and over hundreds of other shacks, including DJ0IP's station, around
> the globe.
>
> Pedantic dogma be hanged !!  I base my claim on 1) real world results,
>  2) TONS of empirical research by others,  and 3) input from my local
> Elmer/guru who designed RF gear for NASA and the AIR FORCE and commercial
> interests.  Mr. B's theory is out of step with the real world.(smiling
> as he typed that, Pardner...)  :-)  -K8JHR-
>
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-- 
--w8lvn--
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Re: [Elecraft] Problem Tuning K3

[Jim Brown]

It should be noted that K8JHR is a lawyer, not an engineer or scientist.

73, Jim K9YC

On 11/4/2021 9:59 AM, JR wrote:

Jim Brown says --

 I suspect you don't understand the physics of
 the problem. OCF antennas are a yesterday's approach
 to multiband antennas. They are a recipe for RX noise
 and RF in the shack.

___

NOT SO, DICK TRACY !


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Re: [Elecraft] Problem Tuning K3

[JR]

Jim Brown says --

I suspect you don't understand the physics of
the problem. OCF antennas are a yesterday's approach
to multiband antennas. They are a recipe for RX noise
and RF in the shack.

___

NOT SO, DICK TRACY !

While YOUR OCF dipole may have problems if poorly deployed and implemented.  It 
is a PLAIN FACT based on thousands of real world examples, OCF Dipoles DO WORK 
WELL.  Mine works very well with NO CMC or other problems.  A few years ago, I 
gave some minor assistance to a notorious German operator, DJ0IP, as he 
collected a wealth of empirical data on CMC and OCF dipoles, carefully testing 
multiple examples before designing a commercial product that has been well 
received by the QRP crowd, receiving positive reviews in the RSGB and ARRL 
magazines.  He received even more assistance from W8JI and G4TXQ and 
others,focusing their attention on how to avoid common mode current (CMC),  
discussing where to offset the feed point, and how to construct a proper 
combination balun and choke.  My OCF Dipole is split 25% /75% split and Rick 
selected a very different feed point, and all is good.

CMC is NOT a necessary evil as Mr. Brown suggests. It CAN be curtailed with "proper 
care and feeding" (pun intended) and the proof flies over my shack, and over 
hundreds of other shacks, including DJ0IP's station, around the globe.

Pedantic dogma be hanged !!  I base my claim on 1) real world results,   2) 
TONS of empirical research by others,  and 3) input from my local Elmer/guru 
who designed RF gear for NASA and the AIR FORCE and commercial interests.  Mr. 
B's theory is out of step with the real world.(smiling as he typed that, 
Pardner...)  :-)  -K8JHR-

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Re: [Elecraft] Problem Tuning K3: now off centre fed dipole

[CUTTER DAVID via Elecraft]

Hi Dan

Good question.  I'll answer as a non-expert as best I can. 

This is essentially a quest for a multi-band dipole that is easy to make and 
use.  If you can put up mono band dipoles and beams for all your bands, you 
probably will not bother going this route. 

The popular description of the ocf dipole (going back at least to the 50's) has 
a feed point of one third/two thirds on the dipole.  (BTW this is otherwise a 
normal half wavelength dipole.

This provides approximately 200 ohm feed point impedance for most popular HF 
bands, eg 80, 40, 20 and 10m, not 15m.  

Back in the 60's we could use coax into a valve PA, which I preferred to the 
G5RV which needed an outboard matching unit.  In transistor days we used a 
modest matching unit with an swr meter and were ignorant of common mode 
current.  
 
In the 90s I used ladder line to ground level and an auto-tuning unit into a 
tent for field day, believing it to be more efficient.   With grounded coax I 
didn't have live chassis syndrome and out in the wilds there was no noise 
pickup.  Later I used ladder line through a balun then into the radio with an 
on-board matching unit and that was, for me a great step forward with 
auto-tuning.  


It was discovered by some users that the common mode current performance using 
off-the-shelf baluns and chokes was inadequate and could result in live chassis 
syndrome and noise pickup on receive from home locations.  Poor matching on 15m 
was still a problem as were the WARC bands. 

Now in the 21st Century, just a few years ago, Rick DJ0IP tackled the problem 
starting with a 40m ocf dipole using a new balun/choke combination.  He read 
that W8JI and others recommended a 20% feedpoint to bring 15m into the 200 ohm 
region. He then used a Guanella 2-core balun solution from Steve G3TXQ and 
others to provide the 50 ohm output with low common mode current.  It had to be 
the dual core version, the single core version simply didn't suppress the cmc.  
This is now marketed by Spiderbeam.  Moving to an 80m version was difficult but 
with a hybrid balun/choke combination he devised a combination that provided at 
least as good cmc and this version is also marketed by Spiderbeam. They both 
work on 15m and some WARC bands. For some layouts a modest on-board matching 
unit is required for complete coverage which is a far cry from bulky outboard 
units; good news for portable operation.  

I would call these *modern* off centre-fed dipoles, ie well into this century.  

I have no financial connection with anyone in that business and I will say that 
I have never seen anyone else produce such a large amount of compelling 
evidence as Rick and I recommend his web site for all things balun and choke 
related to this task.  He takes the practical, non-laboratory approach.  This 
in no way conflicts with any work done by Jim, K9YC and I only wish that he 
would make his own measurements on these modern devices and let go the old 
prejudice.  

73 David G3UNA
  
 




> On 04 November 2021 at 05:24 Dan Presley  wrote:
> 
> 
> Perhaps you could clarify what you meant by a modern OCF. What’s changed from 
> the traditional model? Thanks. 
> 
> Dan Presley 503-701-3871
> danpresley@me. com 
> n7...@arrl.net
>
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Re: [Elecraft] Problem Tuning K3

[Dan Presley]

Perhaps you could clarify what you meant by a modern OCF. What’s changed from 
the traditional model? Thanks. 

Dan Presley 503-701-3871
danpresley@me. com 
n7...@arrl.net


> On Nov 2, 2021, at 12:20, CUTTER DAVID via Elecraft 
>  wrote:
> 
> Hi Jim
> 
> Not many folks have the space or ability to put up a full set of resonant 
> dipoles.  The MODERN off centre fed dipole is as good as you'll get any 
> multiband antenna and for the most part will not need a separate antenna 
> match box.  
> 
> I suggest you measure the common mode current on a decent ocf dipole and see 
> for yourself. Great progress has been made in the last few years and, yes I 
> use your cookbook.  
> 
> David G3UNA
> 
> 
>> On 02 November 2021 at 19:09 Jim Brown  wrote:
>> 
>> 
>>> On 11/2/2021 11:50 AM, CUTTER DAVID wrote:
>>> Don't stay stuck in the past: not all ocf dipoles are created equal.
>>> With properly designed transformers and chokes, the common mode current can 
>>> be tamed to perfectly decent levels.
>> 
>> I suspect you don't understand the physics of the problem. OCF antennas 
>> are a yesterday's approach to multiband antennas. They are a recipe for 
>> RX noise and RF in the shack. The concept was developed decades ago, 
>> when there was far less noise than there is today. It's possible to fool 
>> yourself that it's working fine, but you can't hear very well, so you 
>> miss stations calling you.
>> 
>> I run legal limit on FT8 for weak signal work on 6M and difficult paths 
>> on 160M (EU from California) into resonant antennas that are choked and 
>> fed with RG8 or RG11, and I regularly get signal reports 15-20 dB worse 
>> than I give. Since signal reports on FT8 are signal to noise, that means 
>> the other station can't hear.
>> 
>> 73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3

[CUTTER DAVID via Elecraft]

Hi Jim

Not many folks have the space or ability to put up a full set of resonant 
dipoles.  The MODERN off centre fed dipole is as good as you'll get any 
multiband antenna and for the most part will not need a separate antenna match 
box.  

I suggest you measure the common mode current on a decent ocf dipole and see 
for yourself. Great progress has been made in the last few years and, yes I use 
your cookbook.  

David G3UNA

 
> On 02 November 2021 at 19:09 Jim Brown  wrote:
> 
> 
> On 11/2/2021 11:50 AM, CUTTER DAVID wrote:
> > Don't stay stuck in the past: not all ocf dipoles are created equal.
> > With properly designed transformers and chokes, the common mode current can 
> > be tamed to perfectly decent levels.
> 
> I suspect you don't understand the physics of the problem. OCF antennas 
> are a yesterday's approach to multiband antennas. They are a recipe for 
> RX noise and RF in the shack. The concept was developed decades ago, 
> when there was far less noise than there is today. It's possible to fool 
> yourself that it's working fine, but you can't hear very well, so you 
> miss stations calling you.
> 
> I run legal limit on FT8 for weak signal work on 6M and difficult paths 
> on 160M (EU from California) into resonant antennas that are choked and 
> fed with RG8 or RG11, and I regularly get signal reports 15-20 dB worse 
> than I give. Since signal reports on FT8 are signal to noise, that means 
> the other station can't hear.
> 
> 73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3

[Ray]

Jim…… 
First….. what length is your OCFD ?
2nd……   What Height above ground ?
3rd……   What Feed line are you using ?
4th ……   What Band do you Operate on Most ?
I can Model the Antenna and give you the results .

Ray WA6VAB  K3  


From: CUTTER DAVID via Elecraft
Sent: Tuesday, November 2, 2021 11:50 AM
To: j...@audiosystemsgroup.com; elecraft@mailman.qth.net
Subject: Re: [Elecraft] Problem Tuning K3

Jim

Don't stay stuck in the past: not all ocf dipoles are created equal. 
With properly designed transformers and chokes, the common mode current can be 
tamed to perfectly decent levels.  

David G3UNA

> On 02 November 2021 at 18:25 Jim Brown  wrote:
> 
> 
> On 11/2/2021 6:15 AM, Bill via Elecraft wrote:
> > I assume your using a balun with your
> > OFC antenna. I had a similar problem with my OCF that turned out to be the 
> > balun.  It was fine under low power but would not tune under high power.
> 
> NO! The problem was that by their nature, OCF antennas are BADLY 
> unbalanced, placing very high stress on a common mode choke, so are 
> likely to fry ANY common mode choke that does anything useful.
> 
> Study k9yc.com/RFI-Ham.pdf
> 
> AND -- erase the word "balun" from your vocabulary. It is used to 
> describe almost a dozen very different things, obscuring understanding 
> of how things work.
>
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Re: [Elecraft] Problem Tuning K3

[Jim Brown]

On 11/2/2021 11:50 AM, CUTTER DAVID wrote:

Don't stay stuck in the past: not all ocf dipoles are created equal.
With properly designed transformers and chokes, the common mode current can be 
tamed to perfectly decent levels.


I suspect you don't understand the physics of the problem. OCF antennas 
are a yesterday's approach to multiband antennas. They are a recipe for 
RX noise and RF in the shack. The concept was developed decades ago, 
when there was far less noise than there is today. It's possible to fool 
yourself that it's working fine, but you can't hear very well, so you 
miss stations calling you.


I run legal limit on FT8 for weak signal work on 6M and difficult paths 
on 160M (EU from California) into resonant antennas that are choked and 
fed with RG8 or RG11, and I regularly get signal reports 15-20 dB worse 
than I give. Since signal reports on FT8 are signal to noise, that means 
the other station can't hear.


73, Jim K9YC




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Re: [Elecraft] Problem Tuning K3

[CUTTER DAVID via Elecraft]

Jim

Don't stay stuck in the past: not all ocf dipoles are created equal. 
With properly designed transformers and chokes, the common mode current can be 
tamed to perfectly decent levels.  

David G3UNA

> On 02 November 2021 at 18:25 Jim Brown  wrote:
> 
> 
> On 11/2/2021 6:15 AM, Bill via Elecraft wrote:
> > I assume your using a balun with your
> > OFC antenna. I had a similar problem with my OCF that turned out to be the 
> > balun.  It was fine under low power but would not tune under high power.
> 
> NO! The problem was that by their nature, OCF antennas are BADLY 
> unbalanced, placing very high stress on a common mode choke, so are 
> likely to fry ANY common mode choke that does anything useful.
> 
> Study k9yc.com/RFI-Ham.pdf
> 
> AND -- erase the word "balun" from your vocabulary. It is used to 
> describe almost a dozen very different things, obscuring understanding 
> of how things work.
>
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Re: [Elecraft] Problem Tuning K3

[CUTTER DAVID via Elecraft]

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Re: [Elecraft] Problem Tuning K3

[Jim Brown]

On 11/2/2021 6:15 AM, Bill via Elecraft wrote:

I assume your using a balun with your
OFC antenna. I had a similar problem with my OCF that turned out to be the 
balun.  It was fine under low power but would not tune under high power.


NO! The problem was that by their nature, OCF antennas are BADLY 
unbalanced, placing very high stress on a common mode choke, so are 
likely to fry ANY common mode choke that does anything useful.


Study k9yc.com/RFI-Ham.pdf

AND -- erase the word "balun" from your vocabulary. It is used to 
describe almost a dozen very different things, obscuring understanding 
of how things work.


73, Jim K9YC
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Re: [Elecraft] Problem Tuning K3-" Balun"

[David Gilbert]

A common mode choke (not really a balun) at a point of high SWR can heat 
up and as it does so everything drifts, making tuning impossible.  Been 
there, done that using high power to a 160m Inverted-L that was close to 
resonant, but due to expediency was fed at a point of high SWR.  A 
relayout of the antenna to lower the SWR fixed everything using the same 
choke (which luckily hadn't been permanently damaged).


73,
Dave


From: Bill via Elecraft
Sent: Tuesday, November 2, 2021 6:15 AM
To: elecraft@mailman.qth.net
Subject: [Elecraft] Problem Tuning K3

Jim,
I assume your using a balun with your
OFC antenna. I had a similar problem with my OCF that turned out to be the 
balun.  It was fine under low power but would not tune under high power.

Thanks,
Bill - W0BBI


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Re: [Elecraft] Problem Tuning K3-" Balun"

[Joe Moffatt]

U

Get Outlook for iOS<https://aka.ms/o0ukef>

From: elecraft-boun...@mailman.qth.net  on 
behalf of Ray 
Sent: Tuesday, November 2, 2021 10:00:06 AM
To: bw39...@yahoo.com ; elecraft@mailman.qth.net 

Subject: Re: [Elecraft] Problem Tuning K3-" Balun"

I agree…. Feedline’s Best Friend !
WA6VAB Ray K3


From: Bill via Elecraft
Sent: Tuesday, November 2, 2021 6:15 AM
To: elecraft@mailman.qth.net
Subject: [Elecraft] Problem Tuning K3

Jim,
I assume your using a balun with your
OFC antenna. I had a similar problem with my OCF that turned out to be the 
balun.  It was fine under low power but would not tune under high power.

Thanks,
Bill - W0BBI
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Re: [Elecraft] Problem Tuning K3-" Balun"

[Ray]

I agree…. Feedline’s Best Friend ! 
WA6VAB Ray K3 


From: Bill via Elecraft
Sent: Tuesday, November 2, 2021 6:15 AM
To: elecraft@mailman.qth.net
Subject: [Elecraft] Problem Tuning K3

Jim,
I assume your using a balun with your 
OFC antenna. I had a similar problem with my OCF that turned out to be the 
balun.  It was fine under low power but would not tune under high power. 

Thanks, 
Bill - W0BBI 
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[Elecraft] Problem Tuning K3

[Bill via Elecraft]

Jim,
I assume your using a balun with your 
OFC antenna. I had a similar problem with my OCF that turned out to be the 
balun.  It was fine under low power but would not tune under high power. 

Thanks, 
Bill - W0BBI 
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Re: [Elecraft] Problem Tuning K3

[David Gilbert]

No, that isn't true at all.  FT8 is indeed a WEAK SIGNAL mode, but in no 
way is it limited to low power ... other than the key down capability of 
the rig, of course.  I've used a KW on FT8 on 160m to work Japan and the 
rest of SE Asia in spite of the 2,000 foot high mountain that sits less 
than two miles away from me in direct line to that area.  When using 
high power on FT8 you want to make sure you have a very clean signal, of 
course, but it's a complete fallacy to think that it is strictly a low 
power mode.


Dave   AB7E


On 10/31/2021 3:26 PM, D Remy wrote:

I though FT8 was a superb weak signal mode at 5 to 10 watts at the most.


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Re: [Elecraft] Problem Tuning K3

[D Remy]

Hey Jim!  I though FT8 was a superb weak signal mode at 5 to 10 watts at the 
most.  Nevertheless, I’ve had an inconsistent issue similar to yours.  One 
incident was resolved by backing down on the drive to 20w.  Another time I 
tuned up way off the chosen frequency such that the tuner had to make some 
major change.  Then I went back to near the desired frequency and it re-tuned 
just fine. So, I will be monitoring this thread with great interest to see what 
other responses you get.  73, David, NS4V


David R. Hourdequin, PE
Specialty Heavy Timber Engineer
828-421-6216

> On Oct 31, 2021, at 15:54, Jim Ruff via Elecraft  
> wrote:
> 
> I’m running a K3, KPA500 and a KAT500. My antenna is an 80m OCFD.  When I 
> operate FT8, the rig tunes perfectly on all bands.  When I was operating SSB 
> in the DX contest this weekend, the rig would not tune on any of the SSB 
> frequencies or bands.  If I turned off the KPA500 and the KAT500, the K3 
> would tune all bands and frequencies with it’s internal tuner.  Any ideas on 
> what is causing this to happen?Thanks,Jim W7JHR
> 
> 
> Sent from Yahoo Mail for iPad
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[Elecraft] Problem Tuning K3

[Jim Ruff via Elecraft]

I’m running a K3, KPA500 and a KAT500. My antenna is an 80m OCFD.  When I 
operate FT8, the rig tunes perfectly on all bands.  When I was operating SSB in 
the DX contest this weekend, the rig would not tune on any of the SSB 
frequencies or bands.  If I turned off the KPA500 and the KAT500, the K3 would 
tune all bands and frequencies with it’s internal tuner.  Any ideas on what is 
causing this to happen?Thanks,Jim W7JHR


Sent from Yahoo Mail for iPad
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