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: 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: 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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