[Amps] RF in the Audio

[Jim Barber]

That sounds more like LB Cebik, W4RNL. Jerry Sevick W2FMI never had a 
site of his own that I know of.
You have to dance a jig to get into Cebik's, site, but it can be done 
for free. I don't know if there's a balanced tuner there or not, though:

http://www.cebik.com/

Since my little joke earlier seems to have been a bit obscure for some, 
here's a link to the one I was referring to. Replacing the coax-coil 
choke with something a little more "current" would be an improvement, 
IMHO... (never could resist a pun)

http://www.somis.org/bbat.f2.jpg

Note this doesn't represent the current theoretical discussion here, but 
is a practical example of something that works, regardless of whether or 
not you buy into his other (unrelated) theories or not.

HTH,
Jim N7CXI

On 9/25/2011 1:57 PM, Barrie Smith wrote:
> He passed away a few years ago.  His website is supposed to be still in
> operation and maintained by someone else.
>
> I have no idea where it is.
>
> 73, Barrie, W7ALW
> ----- Original Message -----
> From: "Jim W7RY"<jimw7ry at gmail.com>
> To: "Barrie Smith"<barrie at centric.net>;<amps at contesting.com>
> Sent: Sunday, September 25, 2011 2:51 PM
> Subject: Re: [Amps] RF in the Audio
>
>
>> I don't seem to find his web site.
>>
>> 73
>> Jim W7RY
>>
>>
>> --------------------------------------------------
>> From: "Barrie Smith"<barrie at centric.net>
>> Sent: Sunday, September 25, 2011 11:11 AM
>> To:<amps at contesting.com>
>> Subject: Re: [Amps] RF in the Audio
>>
>>> There's a tutorial on building a "truely-balanced" antenna tuner on
>>> Sevick's
>>> web-site.  Schematics for a practical unit, as well.
>>>
>>> After burning out the balun twice in my MBVA, I built one according to
>>> his
>>> plans.
>>>
>>> Works great.  A balun runs from warm to hot to flames.  My tuner doesn't
>>> even get warm at legal-limit.
>>>
>>> Worth a look.
>>>
>>> 73, Barrie, W7ALW
>>> ----- Original Message -----
>>> From: "Fuqua, Bill L"<wlfuqu00 at uky.edu>
>>> To:<amps at contesting.com>
>>> Sent: Sunday, September 25, 2011 11:20 AM
>>> Subject: Re: [Amps] RF in the Audio
>>>
>>>
>>>>    We can perhaps this forum to come up with some ideas on how to achieve
>>>> a
>>>> goal by new design instead of
>>>> going back and forth with old ideas and currently available equipment.
>>>> bill wa4lav
>>>> ________________________________________
>>>> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On
>>>> Behalf
>>>> Of Fuqua, Bill L [wlfuqu00 at uky.edu]
>>>> Sent: Sunday, September 25, 2011 1:15 PM
>>>> To: amps at contesting.com
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>>    Does anyone make a real balanced line antenna tuner? No  toroidal
>>>> transformer.
>>>>    If I built one I would couple link couple the TX into a tank and link
>>>> couple the output with a swinging
>>>> link with Fariday shield.
>>>>    You could not get any more balanced than that.
>>>>
>>>> 73
>>>> Bill wa4lav
>>>>
>>>> ________________________________________
>>>> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On
>>>> Behalf
>>>> Of Carl [km1h at jeremy.mv.com]
>>>> Sent: Sunday, September 25, 2011 12:14 PM
>>>> To: Rob Atkinson; amps at contesting.com
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>> The last place I would insert a balun is at any point in a OWL fed
>>>> antenna.
>>>>
>>>> Do the twists as have been the norm since the 30's and live with
>>>> whatever
>>>> unbalance remains.
>>>>
>>>> Since OWL theses days assumes the use of a tuner then spend the bucks
>>>> and
>>>> buy/build a truly balanced one especially if running an amp. Compromises
>>>> with QRP and barefoot can get away with a barely functional T200-2 iron
>>>> powder 4:1 balun that comes with the low end tuners.
>>>>
>>>> I always use a LPF between rigs and amps and amps and coax feeds. A 12
>>>> large
>>>> bead sleeve balun of 43 mix is at the input of each LPF and appears more
>>>> than sufficient to keep RF inside the coax on any band. More beads are
>>>> at
>>>> every antenna feed point. All these conform to or are close to the 1000
>>>> Ohm
>>>> impedance rule that has been a sort of ham standard for decades. Im also
>>>> aware of the 1966 CIA document mentioned by K9YC on his site as I was
>>>> Tempest cleared at the highest level at Sanders Associates 1969-78, a
>>>> major
>>>> DoD supplier and deep into stealth technology even back in the 60's. The
>>>> CIA
>>>> and other 3 letter agencies were regular visitors. I didnt remember the
>>>> 5000
>>>> Ohm recommendation however which showed some serious thinking that far
>>>> back.
>>>>
>>>> After eliminating all RFI generators in the house using 2.4" 77 or 31
>>>> mix
>>>> cores over several decades as more junk comes into the house Im assured
>>>> that
>>>> any digital crud heard on the radios is from external sources. The
>>>> HRO-500
>>>> on a 12V battery in the shack and an AM/SW portable as a sniffer have
>>>> been
>>>> used extensively.
>>>>
>>>> Remember also that the initial use of sleeve balun beads was due to TVI
>>>> and
>>>> when a dozen 1" beads could tame any tribander or trap vertical it was
>>>> considered good enough. We didnt have PC's, switchers, digital
>>>> everything
>>>> in
>>>> the house, etc, back then.
>>>>
>>>> Switching Beverages and changing directons of other antennas seems to
>>>> confirm that the sources are thru the air.
>>>>
>>>> I have no use for OWL.
>>>>
>>>> Just last month a new and very loud noise showed up on 160; turns out
>>>> one
>>>> of
>>>> the companies renting tower space changed to a new repeater and required
>>>> several pounds of ferrite to tame.
>>>>
>>>> About 30 years ago I had a friend who owned a 2 way shop ask me to help
>>>> him
>>>> locate an IMD source that was driving him crazy at a repeater site.
>>>> After
>>>> I
>>>> eliminated everything in the building....solid coax and other
>>>> connections,
>>>> no change in recordered VSWR's, etc we sat and studied the display on
>>>> the
>>>> service monitor. Remembering a USN experience from around 1962 I asked
>>>> him
>>>> to go outside and beat on the guy anchors and terminations with a tire
>>>> iron
>>>> from his van. That was the source of the problem, corrosion was causing
>>>> diode joints and rectification of the RF. Back to the house for several
>>>> dozen Snap-On chokes Id been stocking and selling for Yuri, VE3???, and
>>>> they
>>>> were put over the guys and taped in place. No more IMD. Later Yuri
>>>> contracted with RatShak to stock them. Since the 160' tower belonged to
>>>> the
>>>> site owner we were not about to disconnect the guys and use the large
>>>> beads!
>>>> Ive since done that here to all 4 towers.
>>>>
>>>> While K9YC's site has a lot of very good information there is also a bit
>>>> of
>>>> disagreement with what others have published and I dont see that
>>>> changing
>>>> much in my lifetime. He hasnt bothered to reply to my request for a test
>>>> of
>>>> a balun feeding OWL fed dipole covering 160-10M and at 1500W. Lets try
>>>> this
>>>> with a 4:1 and 9:1 as those are the common ones in use as well as
>>>> deliberately varying feed line lengths to present worse case scenarios
>>>> on
>>>> different bands.
>>>>
>>>> One test I rarely see mentioned is to test your coax first.
>>>> Leave in place and terminate the far end in 50 or 75 Ohms and then tune
>>>> the
>>>> bands recording any crud frequencies. Then add a bead balun and
>>>> reterminate.
>>>> Record any differences in signal levels. If you have a quiet receiver
>>>> then
>>>> any pickup with the antenna is likely in "antenna mode" as I like to
>>>> call
>>>> it. Many get confused with all the technical terms used. Any additional
>>>> crud
>>>> picked up in "interference mode" will be small and easily eliminated at
>>>> the
>>>> shack end with another bunch of beads and hopefully a decent RF ground.
>>>> This
>>>> is no different than the Beverage coax procedure as has been in ON4UN's
>>>> Low
>>>> Band DXing and various web pages for awhile.
>>>>
>>>> The expense of DXE or other overpriced Beverage "boxes" is a waste of
>>>> money
>>>> unless you are incapable of following the well documented alternatives
>>>> that
>>>> can be tailored to individual requirements. A one size fits all box can
>>>> have
>>>> a wide range of performance in the real world.
>>>>
>>>> Carl
>>>> KM1H
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Rob Atkinson"<ranchorobbo at gmail.com>
>>>> To:<amps at contesting.com>
>>>> Sent: Sunday, September 25, 2011 8:27 AM
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>>
>>>>> The perceived problem with parallel balanced feedline has nothing to
>>>>> do with the ability to achieve an acceptable balance in the system and
>>>>> everything to do with the way most hams use the line and type of
>>>>> matching network employed.  Roughly 90% of so-called balanced tuners
>>>>> are either non-symmetrical, inadequate in design or (this is the
>>>>> closest to honesty) make no claim of being balanced but somehow claim
>>>>> to handle balanced systems.   The Johnson Matchboxes are genuine
>>>>> balanced tuners that do the job right by putting RF currents in the
>>>>> line that cancel and collapse the field.  I've tested this with my
>>>>> system using current meters and field strength measurements around and
>>>>> in between my line in several random points.  A better tuner is the
>>>>> very hard to fine TMC TAC tuner, probably the best commercially
>>>>> manufactured tuner ever made available to hams.  But many hams express
>>>>> dissatisfaction with the Matchboxes usually over their alleged limited
>>>>> matching range.  That gets us into a separate discussion about the
>>>>> education of hams regarding tuners and their expectations, and is a
>>>>> topic for TowerTalk.
>>>>>
>>>>> The common mode problem exists where you have a balanced system, but a
>>>>> noise point source is closer to one side of the system than the other,
>>>>> so while you have equal and opposite transmit currents, you can have
>>>>> c.m. on receive from a local point source near the antenna, such as
>>>>> noise from a router or power supply in a neighboring home.
>>>>>
>>>>> Jim,
>>>>>
>>>>> I don't think I'd employ DX Engineering as some sort of imprimatur or
>>>>> validator for your work, as they are in the business of making and
>>>>> selling products for hams.
>>>>>
>>>>> Having read the rest of your email, I understand your points and your
>>>>> statements are convincing, on paper at least, but such a choke as you
>>>>> describe seems to be a solution to a problem that doesn't have to
>>>>> exist, if an operator were to employ a method of impedance matching
>>>>> and transfer from balanced feed to unbalanced that would allow for the
>>>>> isolation of the balanced feed to prevent a complete common mode
>>>>> circuit.
>>>>>
>>>>> I can see such a choke being worth a try for someone trying to force a
>>>>> transfer with an unbalanced network, or with one of the symmetrical
>>>>> tuners that contain a pair of synchronized roller inductors and a
>>>>> single common capacitor.  I operated with one of those for a few years
>>>>> and did in fact experience c.m. issues such as conducted out of band
>>>>> RF (a very strong electric service spark gap) detuning a vswr
>>>>> analyzer, but in my case all these problems vanished once I started
>>>>> isolating the balanced feed lines with inductive coupling (the
>>>>> aforementioned Matchboxes).  I believe that is a more robust and
>>>>> reliable solution.
>>>>>
>>>>> 73
>>>>>
>>>>> Rob
>>>>> K5UJ
>>>>>
>>>>>
>>>>>
>>>>> <<<MANY of the DX Engineering so-called baluns are common mode
>>>>> chokes --
>>>>> indeed, what is commonly called a "current balun" IS a common mode
>>>>> choke. Many DXE baluns that transform impedance are ARRAYS of common
>>>>> mode chokes connected in series and parallel.   If you open up some of
>>>>> these you will clearly see chokes would not with coax, but with
>>>>> parallel
>>>>> wires.  And DXE DOES sell a common mode choke. I haven't bought one,
>>>>> because I can rolll my own that are probably better for one-sixth of
>>>>> the
>>>>> cost.
>>>>>
>>>>> I HAVE inserted the bifilar chokes between the output of a Titan 425
>>>>> and
>>>>> the antenna tuner and tested at 1.5kW keydown for several minutes from
>>>>> 1.8 MHz to 28MHz. At that point, the choke sees ONLY the differential
>>>>> field, and there is VERY little heating because the field from one
>>>>> conductor cancels the field from the other.  Dissipation due to common
>>>>> mode current is a very different matter, and is discussed at length in
>>>>> the tutorial. In essence, if the choke as sufficiently choking high
>>>>> impedance and the antenna is not very poorly balanced, the common mode
>>>>> current, and thus the common mode dissipation, is reasonably small.  If
>>>>> conditions of the application (for example, impedance transformation)
>>>>> place very high common mode voltage across a choke, the common mode
>>>>> impedance must be much higher.  In a testing situation, I have set up
>>>>> very high common mode voltages and placed two chokes in series to
>>>>> withstand them.  DXE builds some of their impedance transforming arrays
>>>>> of chokes that way.
>>>>>
>>>>> As to mismatch -- a study of the fundamentals of transmission lines
>>>>> would lead one to the conclusion that the loss due to mismatch in the
>>>>> short length of 100 ohm line that comprises the choke is quite small.
>>>>> After all, one of the most common uses of parallel wire line (notice
>>>>> that I do NOT repeat the fiction of calling it a balanced line) is to
>>>>> minimize the loss due to mismatch when feeding antennas that are wildly
>>>>> mismatched, like the "one-size'fits-all" dipole that is nowhere near
>>>>> resonance on most frequencies where it is used.  Think about this --
>>>>> we're connecting an antenna that could be anything from 5 ohms to 5,000
>>>>> ohms, plus reactance, to a feedline  that is, perhaps, 400 ohms.  The
>>>>> insertion of a 24 inch piece of 100 ohm line simply modifies (and not
>>>>> very much) the impedance of the antenna as seen by the line. And, if
>>>>> wound using #12 copper, as the chokes I have described are, the loss is
>>>>> VERY VERY small, as confirmed by my tests.
>>>>>
>>>>> Now, I'm a guy who plays by the rules, and shares my work FOR those who
>>>>> play by the rules, and my testing is done at that power level, at duty
>>>>> cycles consistent with serious contesting. Someone who wants to run
>>>>> more
>>>>> than 1.5kW can design and test his own solutions. :)
>>>>>
>>>>> 73, Jim Brown K9YC>>
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>> -----
>>>>> No virus found in this message.
>>>>> Checked by AVG - www.avg.com
>>>>> Version: 10.0.1410 / Virus Database: 1520/3917 - Release Date: 09/24/11
>>>>>
>>>>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
> ----- Original Message -----
> From: "Jim W7RY"<jimw7ry at gmail.com>
> To: "Barrie Smith"<barrie at centric.net>;<amps at contesting.com>
> Sent: Sunday, September 25, 2011 2:51 PM
> Subject: Re: [Amps] RF in the Audio
>
>
>> I don't seem to find his web site.
>>
>> 73
>> Jim W7RY
>>
>>
>> --------------------------------------------------
>> From: "Barrie Smith"<barrie at centric.net>
>> Sent: Sunday, September 25, 2011 11:11 AM
>> To:<amps at contesting.com>
>> Subject: Re: [Amps] RF in the Audio
>>
>>> There's a tutorial on building a "truely-balanced" antenna tuner on
>>> Sevick's
>>> web-site.  Schematics for a practical unit, as well.
>>>
>>> After burning out the balun twice in my MBVA, I built one according to
>>> his
>>> plans.
>>>
>>> Works great.  A balun runs from warm to hot to flames.  My tuner doesn't
>>> even get warm at legal-limit.
>>>
>>> Worth a look.
>>>
>>> 73, Barrie, W7ALW
>>> ----- Original Message -----
>>> From: "Fuqua, Bill L"<wlfuqu00 at uky.edu>
>>> To:<amps at contesting.com>
>>> Sent: Sunday, September 25, 2011 11:20 AM
>>> Subject: Re: [Amps] RF in the Audio
>>>
>>>
>>>>    We can perhaps this forum to come up with some ideas on how to achieve
>>>> a
>>>> goal by new design instead of
>>>> going back and forth with old ideas and currently available equipment.
>>>> bill wa4lav
>>>> ________________________________________
>>>> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On
>>>> Behalf
>>>> Of Fuqua, Bill L [wlfuqu00 at uky.edu]
>>>> Sent: Sunday, September 25, 2011 1:15 PM
>>>> To: amps at contesting.com
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>>    Does anyone make a real balanced line antenna tuner? No  toroidal
>>>> transformer.
>>>>    If I built one I would couple link couple the TX into a tank and link
>>>> couple the output with a swinging
>>>> link with Fariday shield.
>>>>    You could not get any more balanced than that.
>>>>
>>>> 73
>>>> Bill wa4lav
>>>>
>>>> ________________________________________
>>>> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On
>>>> Behalf
>>>> Of Carl [km1h at jeremy.mv.com]
>>>> Sent: Sunday, September 25, 2011 12:14 PM
>>>> To: Rob Atkinson; amps at contesting.com
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>> The last place I would insert a balun is at any point in a OWL fed
>>>> antenna.
>>>>
>>>> Do the twists as have been the norm since the 30's and live with
>>>> whatever
>>>> unbalance remains.
>>>>
>>>> Since OWL theses days assumes the use of a tuner then spend the bucks
>>>> and
>>>> buy/build a truly balanced one especially if running an amp. Compromises
>>>> with QRP and barefoot can get away with a barely functional T200-2 iron
>>>> powder 4:1 balun that comes with the low end tuners.
>>>>
>>>> I always use a LPF between rigs and amps and amps and coax feeds. A 12
>>>> large
>>>> bead sleeve balun of 43 mix is at the input of each LPF and appears more
>>>> than sufficient to keep RF inside the coax on any band. More beads are
>>>> at
>>>> every antenna feed point. All these conform to or are close to the 1000
>>>> Ohm
>>>> impedance rule that has been a sort of ham standard for decades. Im also
>>>> aware of the 1966 CIA document mentioned by K9YC on his site as I was
>>>> Tempest cleared at the highest level at Sanders Associates 1969-78, a
>>>> major
>>>> DoD supplier and deep into stealth technology even back in the 60's. The
>>>> CIA
>>>> and other 3 letter agencies were regular visitors. I didnt remember the
>>>> 5000
>>>> Ohm recommendation however which showed some serious thinking that far
>>>> back.
>>>>
>>>> After eliminating all RFI generators in the house using 2.4" 77 or 31
>>>> mix
>>>> cores over several decades as more junk comes into the house Im assured
>>>> that
>>>> any digital crud heard on the radios is from external sources. The
>>>> HRO-500
>>>> on a 12V battery in the shack and an AM/SW portable as a sniffer have
>>>> been
>>>> used extensively.
>>>>
>>>> Remember also that the initial use of sleeve balun beads was due to TVI
>>>> and
>>>> when a dozen 1" beads could tame any tribander or trap vertical it was
>>>> considered good enough. We didnt have PC's, switchers, digital
>>>> everything
>>>> in
>>>> the house, etc, back then.
>>>>
>>>> Switching Beverages and changing directons of other antennas seems to
>>>> confirm that the sources are thru the air.
>>>>
>>>> I have no use for OWL.
>>>>
>>>> Just last month a new and very loud noise showed up on 160; turns out
>>>> one
>>>> of
>>>> the companies renting tower space changed to a new repeater and required
>>>> several pounds of ferrite to tame.
>>>>
>>>> About 30 years ago I had a friend who owned a 2 way shop ask me to help
>>>> him
>>>> locate an IMD source that was driving him crazy at a repeater site.
>>>> After
>>>> I
>>>> eliminated everything in the building....solid coax and other
>>>> connections,
>>>> no change in recordered VSWR's, etc we sat and studied the display on
>>>> the
>>>> service monitor. Remembering a USN experience from around 1962 I asked
>>>> him
>>>> to go outside and beat on the guy anchors and terminations with a tire
>>>> iron
>>>> from his van. That was the source of the problem, corrosion was causing
>>>> diode joints and rectification of the RF. Back to the house for several
>>>> dozen Snap-On chokes Id been stocking and selling for Yuri, VE3???, and
>>>> they
>>>> were put over the guys and taped in place. No more IMD. Later Yuri
>>>> contracted with RatShak to stock them. Since the 160' tower belonged to
>>>> the
>>>> site owner we were not about to disconnect the guys and use the large
>>>> beads!
>>>> Ive since done that here to all 4 towers.
>>>>
>>>> While K9YC's site has a lot of very good information there is also a bit
>>>> of
>>>> disagreement with what others have published and I dont see that
>>>> changing
>>>> much in my lifetime. He hasnt bothered to reply to my request for a test
>>>> of
>>>> a balun feeding OWL fed dipole covering 160-10M and at 1500W. Lets try
>>>> this
>>>> with a 4:1 and 9:1 as those are the common ones in use as well as
>>>> deliberately varying feed line lengths to present worse case scenarios
>>>> on
>>>> different bands.
>>>>
>>>> One test I rarely see mentioned is to test your coax first.
>>>> Leave in place and terminate the far end in 50 or 75 Ohms and then tune
>>>> the
>>>> bands recording any crud frequencies. Then add a bead balun and
>>>> reterminate.
>>>> Record any differences in signal levels. If you have a quiet receiver
>>>> then
>>>> any pickup with the antenna is likely in "antenna mode" as I like to
>>>> call
>>>> it. Many get confused with all the technical terms used. Any additional
>>>> crud
>>>> picked up in "interference mode" will be small and easily eliminated at
>>>> the
>>>> shack end with another bunch of beads and hopefully a decent RF ground.
>>>> This
>>>> is no different than the Beverage coax procedure as has been in ON4UN's
>>>> Low
>>>> Band DXing and various web pages for awhile.
>>>>
>>>> The expense of DXE or other overpriced Beverage "boxes" is a waste of
>>>> money
>>>> unless you are incapable of following the well documented alternatives
>>>> that
>>>> can be tailored to individual requirements. A one size fits all box can
>>>> have
>>>> a wide range of performance in the real world.
>>>>
>>>> Carl
>>>> KM1H
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Rob Atkinson"<ranchorobbo at gmail.com>
>>>> To:<amps at contesting.com>
>>>> Sent: Sunday, September 25, 2011 8:27 AM
>>>> Subject: Re: [Amps] RF in the Audio
>>>>
>>>>
>>>>> The perceived problem with parallel balanced feedline has nothing to
>>>>> do with the ability to achieve an acceptable balance in the system and
>>>>> everything to do with the way most hams use the line and type of
>>>>> matching network employed.  Roughly 90% of so-called balanced tuners
>>>>> are either non-symmetrical, inadequate in design or (this is the
>>>>> closest to honesty) make no claim of being balanced but somehow claim
>>>>> to handle balanced systems.   The Johnson Matchboxes are genuine
>>>>> balanced tuners that do the job right by putting RF currents in the
>>>>> line that cancel and collapse the field.  I've tested this with my
>>>>> system using current meters and field strength measurements around and
>>>>> in between my line in several random points.  A better tuner is the
>>>>> very hard to fine TMC TAC tuner, probably the best commercially
>>>>> manufactured tuner ever made available to hams.  But many hams express
>>>>> dissatisfaction with the Matchboxes usually over their alleged limited
>>>>> matching range.  That gets us into a separate discussion about the
>>>>> education of hams regarding tuners and their expectations, and is a
>>>>> topic for TowerTalk.
>>>>>
>>>>> The common mode problem exists where you have a balanced system, but a
>>>>> noise point source is closer to one side of the system than the other,
>>>>> so while you have equal and opposite transmit currents, you can have
>>>>> c.m. on receive from a local point source near the antenna, such as
>>>>> noise from a router or power supply in a neighboring home.
>>>>>
>>>>> Jim,
>>>>>
>>>>> I don't think I'd employ DX Engineering as some sort of imprimatur or
>>>>> validator for your work, as they are in the business of making and
>>>>> selling products for hams.
>>>>>
>>>>> Having read the rest of your email, I understand your points and your
>>>>> statements are convincing, on paper at least, but such a choke as you
>>>>> describe seems to be a solution to a problem that doesn't have to
>>>>> exist, if an operator were to employ a method of impedance matching
>>>>> and transfer from balanced feed to unbalanced that would allow for the
>>>>> isolation of the balanced feed to prevent a complete common mode
>>>>> circuit.
>>>>>
>>>>> I can see such a choke being worth a try for someone trying to force a
>>>>> transfer with an unbalanced network, or with one of the symmetrical
>>>>> tuners that contain a pair of synchronized roller inductors and a
>>>>> single common capacitor.  I operated with one of those for a few years
>>>>> and did in fact experience c.m. issues such as conducted out of band
>>>>> RF (a very strong electric service spark gap) detuning a vswr
>>>>> analyzer, but in my case all these problems vanished once I started
>>>>> isolating the balanced feed lines with inductive coupling (the
>>>>> aforementioned Matchboxes).  I believe that is a more robust and
>>>>> reliable solution.
>>>>>
>>>>> 73
>>>>>
>>>>> Rob
>>>>> K5UJ
>>>>>
>>>>>
>>>>>
>>>>> <<<MANY of the DX Engineering so-called baluns are common mode
>>>>> chokes --
>>>>> indeed, what is commonly called a "current balun" IS a common mode
>>>>> choke. Many DXE baluns that transform impedance are ARRAYS of common
>>>>> mode chokes connected in series and parallel.   If you open up some of
>>>>> these you will clearly see chokes would not with coax, but with
>>>>> parallel
>>>>> wires.  And DXE DOES sell a common mode choke. I haven't bought one,
>>>>> because I can rolll my own that are probably better for one-sixth of
>>>>> the
>>>>> cost.
>>>>>
>>>>> I HAVE inserted the bifilar chokes between the output of a Titan 425
>>>>> and
>>>>> the antenna tuner and tested at 1.5kW keydown for several minutes from
>>>>> 1.8 MHz to 28MHz. At that point, the choke sees ONLY the differential
>>>>> field, and there is VERY little heating because the field from one
>>>>> conductor cancels the field from the other.  Dissipation due to common
>>>>> mode current is a very different matter, and is discussed at length in
>>>>> the tutorial. In essence, if the choke as sufficiently choking high
>>>>> impedance and the antenna is not very poorly balanced, the common mode
>>>>> current, and thus the common mode dissipation, is reasonably small.  If
>>>>> conditions of the application (for example, impedance transformation)
>>>>> place very high common mode voltage across a choke, the common mode
>>>>> impedance must be much higher.  In a testing situation, I have set up
>>>>> very high common mode voltages and placed two chokes in series to
>>>>> withstand them.  DXE builds some of their impedance transforming arrays
>>>>> of chokes that way.
>>>>>
>>>>> As to mismatch -- a study of the fundamentals of transmission lines
>>>>> would lead one to the conclusion that the loss due to mismatch in the
>>>>> short length of 100 ohm line that comprises the choke is quite small.
>>>>> After all, one of the most common uses of parallel wire line (notice
>>>>> that I do NOT repeat the fiction of calling it a balanced line) is to
>>>>> minimize the loss due to mismatch when feeding antennas that are wildly
>>>>> mismatched, like the "one-size'fits-all" dipole that is nowhere near
>>>>> resonance on most frequencies where it is used.  Think about this --
>>>>> we're connecting an antenna that could be anything from 5 ohms to 5,000
>>>>> ohms, plus reactance, to a feedline  that is, perhaps, 400 ohms.  The
>>>>> insertion of a 24 inch piece of 100 ohm line simply modifies (and not
>>>>> very much) the impedance of the antenna as seen by the line. And, if
>>>>> wound using #12 copper, as the chokes I have described are, the loss is
>>>>> VERY VERY small, as confirmed by my tests.
>>>>>
>>>>> Now, I'm a guy who plays by the rules, and shares my work FOR those who
>>>>> play by the rules, and my testing is done at that power level, at duty
>>>>> cycles consistent with serious contesting. Someone who wants to run
>>>>> more
>>>>> than 1.5kW can design and test his own solutions. :)
>>>>>
>>>>> 73, Jim Brown K9YC>>
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>> -----
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>>>>> Checked by AVG - www.avg.com
>>>>> Version: 10.0.1410 / Virus Database: 1520/3917 - Release Date: 09/24/11
>>>>>
>>>>
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>>>> _______________________________________________
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>>>> _______________________________________________
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>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
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